Navigation transitions: Parse out transiting-entering-color from response headers.
During the navigation transition, after we animate the transition elements, we want to make the background of the transition layer opaque to hide the incoming page load. We set the transition layer's background color to match the outgoing page, and then crossfade to the incoming page's background color for a more seemless transition.
BUG=370696
Review URL: https://codereview.chromium.org/
422153002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286718 0039d316-1c4b-4281-b951-d872f2087c98