Reduce the fullscreen window height by 1px on activation loss and restore it back on activation gain.

This is to workaround a bug/behavior of the Windows taskbar, where in it does not stay as topmost window when a window
on a thread which has a fullscreen window is active. The symptom observed in this case is that the windows on the same thread
as the fullscreen window end up obscuring the taskbar or cause autohide to not work.

The other changes in this patch are as below:-
1. When the bounds of the WinWindow class which serves as
   the PlatformWindow for the WindowTreeHost instance
   change, we don't activate it if the underlying HWND
   is not visible.

2. The WidgetTestInteractive.ViewFocusOnHWNDEnabledChanges
   test explicitly shows the WindowTreeHost instance which
   ensures that the HWND is visible and activated.

BUG=472139
TEST=Covered by views_unittest Widget.FullscreenBoundsReducedOnActivationLoss

Review URL: https://codereview.chromium.org/1707233002

Cr-Commit-Position: refs/heads/master@{#377084}
4 files changed