Add MouseCursorOverlayController.

This controller is heavily based on content::CursorRendererXYZ,
providing the logic for processing platform mouse events and using them
to control the new viz::VideoCaptureOverlay.

In a later CL, this will be integrated with the tab/desktop capture
stack, to complete the migration discussed in crbug 810133.

Bug: 810133,828274
Change-Id: I6502e1ef3cbc878e1c9b062b0abf6a0e6229f860
Reviewed-on: https://chromium-review.googlesource.com/1149264
Reviewed-by: Xiangjun Zhang <xjz@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578079}
7 files changed