Ash: Add resize border shadow effect
* Add ResizeShadow that uses solid-color layers to draw the resize border shadow effect.
* Add ResizeShadowController to create ResizeShadows and track bounds changes for windows.
* Wire both into ToplevelWindowEventFilter to track mouse move/enter events near (but not inside) the window frame.
BUG=118325
TEST=visual, hover mouse near window edges, drag windows
Review URL: https://chromiumcodereview.appspot.com/
9677070
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@127268 0039d316-1c4b-4281-b951-d872f2087c98