Suppress an uninitialized read in isSelfCollapsingBlock.

BUG=334049
TBR=robhogan@gmail.com

Review URL: https://codereview.chromium.org/136553010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244604 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244604