cc: Clean up OcclusionTracker template parameters.

Currently it takes LayerType and RenderSurfaceType, but the latter is
derivable from the former, so just pass the former. Since there's only
one parameter, it's clearer to use OcclusionTracker<Layer(Impl)>
directly instead of using typedefs.

Also rename the TestOcclusionTracker file from
occlusion_tracker_test_common.h to test_occlusion_tracker.h.

R=enne
BUG=344962

Review URL: https://codereview.chromium.org/183563003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254965 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254965