make set3DMask virtual, so we can safely notify the shadercontext

src/core/SkFilterShader.h

Index: src/core/SkFilterShader.h
diff --git a/src/core/SkFilterShader.h b/src/core/SkFilterShader.h
index 2ff6cdaf6359617fd4be21b7c8ba0c76083aa100..b98fc839a6f2a0f36cd29ca2d58cb842d1f231a8 100644
--- a/src/core/SkFilterShader.h
+++ b/src/core/SkFilterShader.h
@@ -30,6 +30,11 @@ public:
         virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
         virtual void shadeSpan16(int x, int y, uint16_t[], int count) SK_OVERRIDE;
 
+        virtual void set3DMask(const SkMask* mask) SK_OVERRIDE {
+            // forward to our proxy
+            fShaderContext->set3DMask(mask);
+        }
+
     private:
         SkShader::Context* fShaderContext;