UnifiedDesktop: mouse warp support
* Refactor utility functions in ExtendedMouseWarpController into display_util.h so that they can be used in both extended and unified mode.
* Move enable flag to MouseWarpControoler.
* Add UnifiedMouseWarpController, which uses MirrorDisplays's window and gfx::Display instead.
- Added support methods in MirrorWindowController.
BUG=365662
TEST=UnifiedMouseWarpControllerTest
Review URL: https://codereview.chromium.org/
1114633002
Cr-Commit-Position: refs/heads/master@{#327671}