Optimize memcheck_analyze.py for ui_tests by using the same log completion waiting scheme as it was before rev47547.
Optimize memcheck_analyze.py for ui_tests
by using the same log completion waiting scheme as it was before rev47547.

Before 47547:
memcheck_analyze.Analyze was called once for all log files.
That means, wait 3 minutes max in total for logs to complete.

After 47547:
memcheck_analyze.Analyze is called once for each ui_test. (better logs)
That means, wait 3 minutes max for each ui_test and there are many of them. (SLOW!!!)

After this patch:
memcheck_analyze.Analyze is called once for each ui_test. (better logs)
But since AnalyzeStartTime is now global,
we wait 3 minutes max in total for logs to complete.

TEST=Valgrind/UI bots should become faster
Review URL: http://codereview.chromium.org/3035025

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@53613 0039d316-1c4b-4281-b951-d872f2087c98

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