GitLab

The problem is that CrxInstaller wasn't considering updates when looking for
previously installed apps with overlapping extents.

BUG=68872
TEST=Steps outlined in bug report. 

Review URL: http://codereview.chromium.org/6292007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71818 0039d316-1c4b-4281-b951-d872f2087c98