Disable cursor compositing when virtual keyboard is enabled.

BUG=347009
TEST=verify cursor is not obscured by virtual keyboard.
R=oshima@chromium.org

Review URL: https://codereview.chromium.org/181003004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253605 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253605