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In ozone/x11, the region is set to a non-rectangular shape from
GetDefaultWindowMask for the rounded corner of browser frame.
The window region is updated in XWindow::UpdateWindowRegion and
sets in shape of X11 ExtensionManager.

In ozone/wayland, it doesn't get any shape information
from the platform window.

In this CL,
- Introduce PlatformWindowDelegate::GetWindowMaskForWindowShape to get
  the window mask information.
- Create |window_shape_| from window mask for non-rectangular window
  shape.
- Create region from |window_shape_| if it exists and set opaque/input
  region.
- Update |window_shape_| and update opaque/input region

Bug: 1126828
Change-Id: I56c928986526b88cd4b2c5e8fc3b4921f50a372c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2578501Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Maksim Sisov <msisov@igalia.com>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Commit-Queue: MINJU KIM <mkim@igalia.com>
Cr-Commit-Position: refs/heads/master@{#841778}