Add allocator dependency to events_unittests.

TEST=linux/heapcheck bot
R=glider@chromium.org, sadrul@chromium.org
BUG=

Review URL: https://codereview.chromium.org/94103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237760 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237760