Make the member |is_cursor_visible_| in DesktopWindowTreeHostWin static.

On Windows we can have multiple root windows and the implementation
of ::ShowCursor() is based on a counter, so making this member static
ensures that ::ShowCursor() is always called exactly once whenever the
cursor visibility state changes. This prevents an incorrectly hidden
(or incorrectly shown) cursor because the number of calls to
::ShowCursor() is no longer dependent on the number of instantiated
root windows at the time when a request to change the cursor visibility
is made.

BUG=317496

Review URL: https://codereview.chromium.org/151563004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249310 0039d316-1c4b-4281-b951-d872f2087c98
Update base/BUILD.gn for dicardable memory changes

TBR=scottmg

Review URL: https://codereview.chromium.org/147683005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249311 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249310
SVN changes up to revision 249311