Fix crash in TraceLog::UpdateTraceEventDuration()
Because we don't lock when getting event_callback_, there will be
chance that it has been set to NULL in SetEventCallbackDisabled()
in another thread, but category_group_enabled has not been updated yet.
Always check if event_callback is NULL before calling it.
BUG=323016
TBR=nduca
NOTRY=true
Review URL: https://codereview.chromium.org/84963007
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237096 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed
