Get lastchange.py to work correctly on Git repositories.
Get lastchange.py to work correctly on Git repositories.

This changes lastchange.py in two ways:
1) If the commit it finds is a Git hash, it outputs the whole hash, not just
   the first 7 characters.
2) It only looks at HEAD to see if there is a git-svn id. Previously, it used
   --grep=git-svn-id, which would find the most recent commit containing a
   git-svn id. This would be broken after the switch to git, as it would always
   find the last commit before the switch. Now, it only inspects the most recent
   commit, and falls through to pure-Git if that fails.

R=dilmah@chromium.org, stip@chromium.org
BUG=399113

Review URL: https://codereview.chromium.org/488733002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#291165}
git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@291165 0039d316-1c4b-4281-b951-d872f2087c98

Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Just-D/chromium-1,dushu1203/chromium.src,dednal/chromium.src,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,fujunwei/chromium-crosswalk,dushu1203/chromium.src,PeterWangIntel/chromium-crosswalk,krieger-od/nwjs_chromium.src,Just-D/chromium-1,fujunwei/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,axinging/chromium-crosswalk,hgl888/chromium-crosswalk,M4sse/chromium.src,Fireblend/chromium-crosswalk,ltilve/chromium,Fireblend/chromium-crosswalk,Fireblend/chromium-crosswalk,markYoungH/chromium.src,dednal/chromium.src,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,Jonekee/chromium.src,markYoungH/chromium.src,M4sse/chromium.src,hgl888/chromium-crosswalk-efl,Jonekee/chromium.src,markYoungH/chromium.src,axinging/chromium-crosswalk,krieger-od/nwjs_chromium.src,markYoungH/chromium.src,hgl888/chromium-crosswalk-efl,TheTypoMaster/chromium-crosswalk,markYoungH/chromium.src,Fireblend/chromium-crosswalk,M4sse/chromium.src,TheTypoMaster/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,dednal/chromium.src,ltilve/chromium,fujunwei/chromium-crosswalk,markYoungH/chromium.src,chuan9/chromium-crosswalk,krieger-od/nwjs_chromium.src,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,markYoungH/chromium.src,ltilve/chromium,M4sse/chromium.src,Chilledheart/chromium,crosswalk-project/chromium-crosswalk-efl,mohamed--abdel-maksoud/chromium.src,hgl888/chromium-crosswalk,dushu1203/chromium.src,dushu1203/chromium.src,chuan9/chromium-crosswalk,hgl888/chromium-crosswalk-efl,markYoungH/chromium.src,Chilledheart/chromium,PeterWangIntel/chromium-crosswalk,M4sse/chromium.src,crosswalk-project/chromium-crosswalk-efl,Chilledheart/chromium,hgl888/chromium-crosswalk,jaruba/chromium.src,axinging/chromium-crosswalk,markYoungH/chromium.src,dednal/chromium.src,dushu1203/chromium.src,dushu1203/chromium.src,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,dushu1203/chromium.src,hgl888/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,ltilve/chromium,ltilve/chromium,hgl888/chromium-crosswalk-efl,Jonekee/chromium.src,Pluto-tv/chromium-crosswalk,chuan9/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,krieger-od/nwjs_chromium.src,mohamed--abdel-maksoud/chromium.src,dednal/chromium.src,M4sse/chromium.src,Jonekee/chromium.src,Pluto-tv/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,crosswalk-project/chromium-crosswalk-efl,jaruba/chromium.src,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,fujunwei/chromium-crosswalk,hgl888/chromium-crosswalk-efl,fujunwei/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,PeterWangIntel/chromium-crosswalk,dushu1203/chromium.src,chuan9/chromium-crosswalk,M4sse/chromium.src,axinging/chromium-crosswalk,ltilve/chromium,chuan9/chromium-crosswalk,M4sse/chromium.src,jaruba/chromium.src,mohamed--abdel-maksoud/chromium.src,dushu1203/chromium.src,krieger-od/nwjs_chromium.src,dednal/chromium.src,Jonekee/chromium.src,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk,Pluto-tv/chromium-crosswalk,fujunwei/chromium-crosswalk,Just-D/chromium-1,hgl888/chromium-crosswalk-efl,Chilledheart/chromium,Chilledheart/chromium,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,dednal/chromium.src,mohamed--abdel-maksoud/chromium.src,dushu1203/chromium.src,crosswalk-project/chromium-crosswalk-efl,fujunwei/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Just-D/chromium-1,Jonekee/chromium.src,dushu1203/chromium.src,ltilve/chromium,M4sse/chromium.src,M4sse/chromium.src,TheTypoMaster/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,fujunwei/chromium-crosswalk,dednal/chromium.src,axinging/chromium-crosswalk,jaruba/chromium.src,Jonekee/chromium.src,Jonekee/chromium.src,Just-D/chromium-1,Chilledheart/chromium,hgl888/chromium-crosswalk,jaruba/chromium.src,dednal/chromium.src,hgl888/chromium-crosswalk-efl,chuan9/chromium-crosswalk,Pluto-tv/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,axinging/chromium-crosswalk,dednal/chromium.src,Chilledheart/chromium,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,chuan9/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,M4sse/chromium.src,Fireblend/chromium-crosswalk,hgl888/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,jaruba/chromium.src,PeterWangIntel/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,axinging/chromium-crosswalk,dednal/chromium.src,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk-efl,jaruba/chromium.src,Pluto-tv/chromium-crosswalk,jaruba/chromium.src,Just-D/chromium-1,axinging/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,hgl888/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,markYoungH/chromium.src,hgl888/chromium-crosswalk,Just-D/chromium-1,Fireblend/chromium-crosswalk,krieger-od/nwjs_chromium.src,ltilve/chromium,mohamed--abdel-maksoud/chromium.src,markYoungH/chromium.src,Jonekee/chromium.src,jaruba/chromium.src,TheTypoMaster/chromium-crosswalk,Just-D/chromium-1,ltilve/chromium,fujunwei/chromium-crosswalk,Jonekee/chromium.src,Fireblend/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,jaruba/chromium.src,Jonekee/chromium.src,jaruba/chromium.src