cc: Clean up iterator template to only take 1 parameter.

LayerIterator takes 4 parameters. One is the FrontToBack ordering
but that is now the only option. The other 3 are for the type of layers,
render surfaces, and the render surface layer list. The latter two are
now already available as typedefs off of Layer and LayerImpl, so we
only need Layer/LayerImpl in the template arguments.

R=enne@chromium.org, enne
BUG=YAK

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251238

Review URL: https://codereview.chromium.org/156603005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254156 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254156