Allow GrGLEffects to produce variable length keys.

src/effects/SkLumaColorFilter.cpp

Index: src/effects/SkLumaColorFilter.cpp
diff --git a/src/effects/SkLumaColorFilter.cpp b/src/effects/SkLumaColorFilter.cpp
index 7564307f45efd214b33dc82cba68d2fb1400b5fd..d33e5e8d78ea0087c2fc9ded6656b797afa0ddde 100644
--- a/src/effects/SkLumaColorFilter.cpp
+++ b/src/effects/SkLumaColorFilter.cpp
@@ -86,14 +86,11 @@ public:
         : INHERITED(factory) {
         }
 
-        static EffectKey GenKey(const GrDrawEffect&, const GrGLCaps&) {
-            // this class always generates the same code.
-            return 0;
-        }
+        static void GenKey(const GrDrawEffect&, const GrGLCaps&, GrEffectKeyBuilder* b) {}
 
         virtual void emitCode(GrGLShaderBuilder* builder,
                               const GrDrawEffect&,
-                              EffectKey,
+                              const GrEffectKey&,
                               const char* outputColor,
                               const char* inputColor,
                               const TransformedCoordsArray&,