Add a GrCustomCoordsTextureEffect class

Extracts a GrCustomCoordsTextureEffect class from
GrSimpleTextureEffect. This way there are no effects that can
conditionally require a vertex shader. They either always need one or
never do. Also removes kCustom_CoordsType from the CoordsType enum in
GrEffect (that enum is really only meant for coords provided by the
framework), and updates GrSimpleTextureEffect::TestCreate to make the
effect with position as well, instead of just local coords.


Review URL:

git-svn-id: 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/GrEffect.h b/gpu/GrEffect.h
index 78ad28b..e7590b6 100644
--- a/gpu/GrEffect.h
+++ b/gpu/GrEffect.h
@@ -85,15 +85,11 @@
      * The types of vertex coordinates available to an effect in the vertex shader. Effects can
      * require their own vertex attribute but these coordinates are made available by the framework
-     * in all programs. kCustom_CoordsType is provided to signify that an alternative set of coords
-     * is used (usually an explicit vertex attribute) but its meaning is determined by the effect
-     * subclass.
+     * in all programs.
     enum CoordsType {
-        kCustom_CoordsType,
     virtual ~GrEffect();