Push isEqual/onIsEqual down from GrProcessor to subclasses.

R=joshualitt@google.com

Review URL: https://codereview.chromium.org/654273002
diff --git a/src/gpu/effects/GrMatrixConvolutionEffect.h b/src/gpu/effects/GrMatrixConvolutionEffect.h
index c653230..5aee6c5 100644
--- a/src/gpu/effects/GrMatrixConvolutionEffect.h
+++ b/src/gpu/effects/GrMatrixConvolutionEffect.h
@@ -77,7 +77,7 @@
                               GrTextureDomain::Mode tileMode,
                               bool convolveAlpha);
 
-    virtual bool onIsEqual(const GrProcessor&) const SK_OVERRIDE;
+    virtual bool onIsEqual(const GrFragmentProcessor&) const SK_OVERRIDE;
 
     virtual void onComputeInvariantOutput(InvariantOutput* inout) const SK_OVERRIDE {
         // TODO: Try to do better?