Fix the issue of cursor being shown at startup.
Cursor was shown by MagnificationController when it's enabled in chrome::OpenAsh.
This CL makes MagnificationController not to show cursor if unnecessary.
Also makes cursor initially hidden when the host window is not using full screen
for testing ChromeOS build on desktop.
BUG=157918
TEST=Manually on device and desktop
Review URL: https://chromiumcodereview.appspot.com/
11364003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168830 0039d316-1c4b-4281-b951-d872f2087c98