Extract most of the mutable state of SkShader into a separate Context object.

src/core/SkFilterShader.h

Index: src/core/SkFilterShader.h
diff --git a/src/core/SkFilterShader.h b/src/core/SkFilterShader.h
index 11add0cf17c6304da59e9baf0289bfe04ad5a98c..4ef45772482bf0cf6d7e06730bd9dc0378ac8fc0 100644
--- a/src/core/SkFilterShader.h
+++ b/src/core/SkFilterShader.h
@@ -17,12 +17,29 @@ public:
     SkFilterShader(SkShader* shader, SkColorFilter* filter);
     virtual ~SkFilterShader();
 
-    virtual uint32_t getFlags() SK_OVERRIDE;
-    virtual bool setContext(const SkBitmap&, const SkPaint&,
-                            const SkMatrix&) SK_OVERRIDE;
-    virtual void endContext() SK_OVERRIDE;
-    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 bool validContext(const SkBitmap&, const SkPaint&,
+                              const SkMatrix&, SkMatrix* totalInverse = NULL) const SK_OVERRIDE;
+    virtual SkShader::Context* createContext(const SkBitmap&, const SkPaint&,
+                                             const SkMatrix&, void* storage) const SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE;
+
+    class FilterShaderContext : public SkShader::Context {
+    public:
+        // Takes ownership of shaderContext and calls its destructor.
+        FilterShaderContext(const SkFilterShader& filterShader, SkShader::Context* shaderContext,
+                            const SkBitmap& device, const SkPaint& paint, const SkMatrix& matrix);
+        virtual ~FilterShaderContext();
+
+        virtual uint32_t getFlags() const SK_OVERRIDE;
+
+        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;
+
+    private:
+        SkShader::Context* fShaderContext;
+
+        typedef SkShader::Context INHERITED;
+    };
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkFilterShader)