Add edge gesture so you can easily go from fullscreen and back. Currently you can go into fullscreen via he wrench menu but cannot go out of fullscreen because the edge allowance is not enough.

This btw the same behavior we have since m26 for metro.

BUG=174738

Review URL: https://codereview.chromium.org/73063002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235844 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235844