[Telemetry] Make unhandled exception output more useful.
[Telemetry] Make unhandled exception output more useful.

This should help tremendously in diagnosing flake on the bots.

Default format:
---------------------------
Traceback (most recent call last):
  File "tools/perf/run_benchmark", line 23, in <module>
    sys.exit(test_runner.Main())
  File "tools/perf/../telemetry/telemetry/test_runner.py", line 290, in Main
    return command.Run(options, args)
  File "tools/perf/../telemetry/telemetry/test_runner.py", line 198, in Run
    return min(255, self._test().Run(copy.copy(options)))
  File "tools/perf/../telemetry/telemetry/test.py", line 53, in Run
    results = page_runner.Run(test, ps, expectations, options)
  File "tools/perf/../telemetry/telemetry/page/page_runner.py", line 330, in Run
    possible_browser, results, state)
  File "tools/perf/../telemetry/telemetry/page/page_runner.py", line 213, in _PrepareAndRunPage
    credentials_path, page.archive_path)
  File "tools/perf/../telemetry/telemetry/page/page_runner.py", line 54, in StartBrowser
    test.DidStartBrowser(self.browser)
  File "/work/chromium/src/tools/perf/measurements/page_cycler.py", line 71, in DidStartBrowser
    self._memory_metric = memory.MemoryMetric(browser)
  File "/work/chromium/src/tools/perf/metrics/memory.py", line 32, in __init__
    self._start_commit_charge = self._browser.memory_stats['SystemCommitCharge']
  File "tools/perf/../telemetry/telemetry/core/browser.py", line 166, in memory_stats
    result = self._GetStatsCommon(self._platform_backend.GetMemoryStats)
  File "tools/perf/../telemetry/telemetry/core/browser.py", line 99, in _GetStatsCommon
    for child_pid in self._platform_backend.GetChildPids(browser_pid):
  File "tools/perf/../telemetry/telemetry/core/platform/posix_platform_backend.py", line 44, in GetChildPids
    return proc_util.GetChildPids(processes, pid)
  File "tools/perf/../telemetry/telemetry/core/platform/proc_util.py", line 86, in GetChildPids
    for foo, curr_pid, curr_ppid, state in processes:
ValueError: need more than 3 values to unpack
---------------------------

New format:
---------------------------
Traceback (most recent call last):
  <module> at tools/perf/run_benchmark:23
    sys.exit(test_runner.Main())
  Main at tools/telemetry/telemetry/test_runner.py:303
    return command.Run(options, args)
  Run at tools/telemetry/telemetry/test_runner.py:211
    return min(255, self._test().Run(copy.copy(options)))
  Run at tools/telemetry/telemetry/test.py:53
    results = page_runner.Run(test, ps, expectations, options)
  Run at tools/telemetry/telemetry/page/page_runner.py:330
    possible_browser, results, state)
  _PrepareAndRunPage at tools/telemetry/telemetry/page/page_runner.py:213
    credentials_path, page.archive_path)
  StartBrowser at tools/telemetry/telemetry/page/page_runner.py:54
    test.DidStartBrowser(self.browser)
  DidStartBrowser at tools/perf/measurements/page_cycler.py:71
    self._memory_metric = memory.MemoryMetric(browser)
  __init__ at tools/perf/metrics/memory.py:32
    self._start_commit_charge = self._browser.memory_stats['SystemCommitCharge']
  memory_stats at tools/telemetry/telemetry/core/browser.py:166
    result = self._GetStatsCommon(self._platform_backend.GetMemoryStats)
  _GetStatsCommon at tools/telemetry/telemetry/core/browser.py:99
    for child_pid in self._platform_backend.GetChildPids(browser_pid):
  GetChildPids at tools/telemetry/telemetry/core/platform/posix_platform_backend.py:44
    return proc_util.GetChildPids(processes, pid)
  GetChildPids at tools/telemetry/telemetry/core/platform/proc_util.py:86
    for foo, curr_pid, curr_ppid, state in processes:

Locals:
  child_dict : defaultdict(<type 'list'>, {})
  pid        : 5510
  processes  : [['1', '0', 'Ss'], ['15', '1', 'Ss'], ['16', '1', 'Ss'], ['17 ... 99', 'R+'], ['78347', '78344', 'Ss'], ['78349', '78347', 'S']] (truncated)

ValueError: need more than 3 values to unpack
---------------------------

BUG=

Review URL: https://codereview.chromium.org/64553004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@234648 0039d316-1c4b-4281-b951-d872f2087c98

patrickm/chromium.src,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,patrickm/chromium.src,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,jaruba/chromium.src,ltilve/chromium,Jonekee/chromium.src,Chilledheart/chromium,axinging/chromium-crosswalk,dednal/chromium.src,krieger-od/nwjs_chromium.src,Just-D/chromium-1,ChromiumWebApps/chromium,markYoungH/chromium.src,jaruba/chromium.src,axinging/chromium-crosswalk,krieger-od/nwjs_chromium.src,Just-D/chromium-1,anirudhSK/chromium,patrickm/chromium.src,bright-sparks/chromium-spacewalk,dednal/chromium.src,PeterWangIntel/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,krieger-od/nwjs_chromium.src,Jonekee/chromium.src,littlstar/chromium.src,bright-sparks/chromium-spacewalk,anirudhSK/chromium,ChromiumWebApps/chromium,Jonekee/chromium.src,ltilve/chromium,bright-sparks/chromium-spacewalk,patrickm/chromium.src,Pluto-tv/chromium-crosswalk,jaruba/chromium.src,ChromiumWebApps/chromium,axinging/chromium-crosswalk,dushu1203/chromium.src,Chilledheart/chromium,hgl888/chromium-crosswalk-efl,Fireblend/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,dednal/chromium.src,markYoungH/chromium.src,Fireblend/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,dushu1203/chromium.src,jaruba/chromium.src,fujunwei/chromium-crosswalk,hgl888/chromium-crosswalk,ondra-novak/chromium.src,Chilledheart/chromium,patrickm/chromium.src,Fireblend/chromium-crosswalk,M4sse/chromium.src,chuan9/chromium-crosswalk,ltilve/chromium,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,markYoungH/chromium.src,markYoungH/chromium.src,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk,hgl888/chromium-crosswalk,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,ChromiumWebApps/chromium,hgl888/chromium-crosswalk-efl,ChromiumWebApps/chromium,dednal/chromium.src,Just-D/chromium-1,Chilledheart/chromium,ondra-novak/chromium.src,Fireblend/chromium-crosswalk,littlstar/chromium.src,bright-sparks/chromium-spacewalk,crosswalk-project/chromium-crosswalk-efl,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk-efl,Just-D/chromium-1,ondra-novak/chromium.src,mohamed--abdel-maksoud/chromium.src,anirudhSK/chromium,ChromiumWebApps/chromium,ltilve/chromium,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,ChromiumWebApps/chromium,ChromiumWebApps/chromium,TheTypoMaster/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,M4sse/chromium.src,littlstar/chromium.src,fujunwei/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Chilledheart/chromium,anirudhSK/chromium,M4sse/chromium.src,mohamed--abdel-maksoud/chromium.src,dednal/chromium.src,mohamed--abdel-maksoud/chromium.src,ChromiumWebApps/chromium,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,dednal/chromium.src,jaruba/chromium.src,krieger-od/nwjs_chromium.src,axinging/chromium-crosswalk,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk,anirudhSK/chromium,ltilve/chromium,dednal/chromium.src,Jonekee/chromium.src,littlstar/chromium.src,hgl888/chromium-crosswalk-efl,crosswalk-project/chromium-crosswalk-efl,axinging/chromium-crosswalk,anirudhSK/chromium,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,markYoungH/chromium.src,markYoungH/chromium.src,Jonekee/chromium.src,dushu1203/chromium.src,ondra-novak/chromium.src,Chilledheart/chromium,hgl888/chromium-crosswalk-efl,mohamed--abdel-maksoud/chromium.src,patrickm/chromium.src,hgl888/chromium-crosswalk-efl,PeterWangIntel/chromium-crosswalk,jaruba/chromium.src,dushu1203/chromium.src,dushu1203/chromium.src,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,dushu1203/chromium.src,Just-D/chromium-1,ondra-novak/chromium.src,hgl888/chromium-crosswalk,krieger-od/nwjs_chromium.src,ondra-novak/chromium.src,anirudhSK/chromium,Jonekee/chromium.src,Fireblend/chromium-crosswalk,anirudhSK/chromium,M4sse/chromium.src,axinging/chromium-crosswalk,ChromiumWebApps/chromium,dushu1203/chromium.src,PeterWangIntel/chromium-crosswalk,ChromiumWebApps/chromium,Jonekee/chromium.src,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk-efl,Chilledheart/chromium,bright-sparks/chromium-spacewalk,M4sse/chromium.src,krieger-od/nwjs_chromium.src,M4sse/chromium.src,patrickm/chromium.src,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,chuan9/chromium-crosswalk,chuan9/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,TheTypoMaster/chromium-crosswalk,dushu1203/chromium.src,TheTypoMaster/chromium-crosswalk,M4sse/chromium.src,krieger-od/nwjs_chromium.src,axinging/chromium-crosswalk,Just-D/chromium-1,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,ltilve/chromium,Jonekee/chromium.src,hgl888/chromium-crosswalk,Just-D/chromium-1,bright-sparks/chromium-spacewalk,mohamed--abdel-maksoud/chromium.src,jaruba/chromium.src,dushu1203/chromium.src,dednal/chromium.src,M4sse/chromium.src,krieger-od/nwjs_chromium.src,markYoungH/chromium.src,M4sse/chromium.src,hgl888/chromium-crosswalk-efl,markYoungH/chromium.src,PeterWangIntel/chromium-crosswalk,ltilve/chromium,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,dednal/chromium.src,Pluto-tv/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,hgl888/chromium-crosswalk,Fireblend/chromium-crosswalk,krieger-od/nwjs_chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,markYoungH/chromium.src,dushu1203/chromium.src,crosswalk-project/chromium-crosswalk-efl,patrickm/chromium.src,M4sse/chromium.src,Just-D/chromium-1,ltilve/chromium,crosswalk-project/chromium-crosswalk-efl,dushu1203/chromium.src,markYoungH/chromium.src,ChromiumWebApps/chromium,jaruba/chromium.src,PeterWangIntel/chromium-crosswalk,Chilledheart/chromium,Just-D/chromium-1,anirudhSK/chromium,M4sse/chromium.src,Chilledheart/chromium,Jonekee/chromium.src,jaruba/chromium.src,jaruba/chromium.src,Jonekee/chromium.src,mohamed--abdel-maksoud/chromium.src,mohamed--abdel-maksoud/chromium.src,littlstar/chromium.src,dednal/chromium.src,hgl888/chromium-crosswalk-efl,littlstar/chromium.src,dednal/chromium.src,jaruba/chromium.src,hgl888/chromium-crosswalk-efl,Jonekee/chromium.src,chuan9/chromium-crosswalk,Fireblend/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,fujunwei/chromium-crosswalk,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,ltilve/chromium,littlstar/chromium.src,chuan9/chromium-crosswalk,markYoungH/chromium.src,TheTypoMaster/chromium-crosswalk,krieger-od/nwjs_chromium.src,TheTypoMaster/chromium-crosswalk,ondra-novak/chromium.src,patrickm/chromium.src,mohamed--abdel-maksoud/chromium.src,anirudhSK/chromium