GitLab

This is part 1 of implemeting phantom windows for the window controls when using --ash-enable-alternate-caption-button

Other notable changes:
- Switched to using layer animations instead of gfx::SlideAnimation
- Renamed PhantomWindowController::phantom_widget_ and PhantomWindowController::phantom_widget_start_ to PhantomWindowController::phantom_widget_in_target_root_ and PhantomWindowController::phantom_widget_in_start_root_ respectively.
- Removed PhantomWindowController::Hide(). Hiding the phantom window can now only be done via destroying the PhantomWindowController

BUG=328930
TEST=PhantomWindowControllerTest.*

Review URL: https://codereview.chromium.org/101773004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244050 0039d316-1c4b-4281-b951-d872f2087c98