Implement cursor compositing mode on Ash

Currently this is only enabled when the accessibility feature
"high contrast" mode or "large cursor" mode is enabled.

We do not enable this by default because cursor compositing
shows some lags especially on slow machines or when CPU is busy.

BUG=290837
TEST=trybot, manual testing mirror/extend/dual display mode
R=derat@chromium.org, oshima@chromium.org

Review URL: https://codereview.chromium.org/145313003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249289 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249289