Implement color filter as GrGLEffect

include/gpu/GrEffect.h

Index: include/gpu/GrEffect.h
diff --git a/include/gpu/GrEffect.h b/include/gpu/GrEffect.h
index 4dc294bfe8a1bbd49de162fe63b7dc1ba476f6f3..5bde6fad6a278e057e45be720bcb480c828f1543 100644
--- a/include/gpu/GrEffect.h
+++ b/include/gpu/GrEffect.h
@@ -104,6 +104,9 @@ public:
      */
     virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const = 0;
 
+    /** Will this effect read the source color value? */
+    virtual bool willUseInputColor() const { return true; }
+
     /** This object, besides creating back-end-specific helper objects, is used for run-time-type-
         identification. The factory should be an instance of templated class,
         GrTBackendEffectFactory. It is templated on the subclass of GrEffect. The subclass must have