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 78752702f549bbd8296379e093e0e14ca428c06e..e70a1c71311c36b44b0bf91e4c3f140aee2d3cd0 100644
--- a/include/gpu/GrEffect.h
+++ b/include/gpu/GrEffect.h
@@ -95,6 +95,9 @@ 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