libwebp: cherry-pick lossless signature check improvement

92d47e4 improve VP8L signature detection by checking the version bits too

BUG=

Review URL: https://codereview.chromium.org/25563003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226447 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226447
Disable TabStripModelTest.FastShutdown on DrMemory.

BUG=302156
TBR=glider@chromium.org

Review URL: https://codereview.chromium.org/25665005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226448 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226448