GitLab

- Add ConstrainedWindowViewTest.BackspaceSentToWebContent for Aura.
- Add ConstrainedWindowViewTest.EscapeCloseConstrainedWindow, which verifies that escape key closes the constrained window.
- Extract TestWindowObserver to ui/views/test from bubble_delegate_unittest.cc

BUG=156437

Review URL: https://codereview.chromium.org/11639012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175739 0039d316-1c4b-4281-b951-d872f2087c98