exit from main instead of returning.  Defeats tail call optimization that makes it look like start calls ChromeMain directly, because nobody's got symbols for start.
exit from main instead of returning.  Defeats tail call optimization that
makes it look like start calls ChromeMain directly, because nobody's got
symbols for start.

BUG=39232
TEST=Breakpad reports should show thread 0 beginning in main
Review URL: http://codereview.chromium.org/1457001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@42803 0039d316-1c4b-4281-b951-d872f2087c98

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