Make specifying a texture optional on a Layer.

This is for Layers that participate in Draw() ordering, transforming and clipping, but do not themselves actually render anything.

Also changes LayerTest to use RunAllPending() rather than using the weird QuitOnComposited test type I had.

BUG=none
TEST=see unittest
Review URL: http://codereview.chromium.org/7941016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@101829 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed