extend SkShader to report a luminance-color to be used for gamma correction

include/core/SkColorShader.h

-
 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-
 #ifndef SkColorShader_DEFINED
 #define SkColorShader_DEFINED
 
 #include "SkShader.h"
 
 /** \class SkColorShader
     A Shader that represents a single color. In general, this effect can be
     accomplished by just using the color field on the paint, but if an
     actual shader object is needed, this provides that feature.
 */
@@ skipping 40 matching lines @@
                              const SkMatrix* localMatrix, GrColor* paintColor,
                              GrEffect** effect) const SK_OVERRIDE;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkColorShader)
 
 protected:
     SkColorShader(SkReadBuffer&);
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
     virtual Context* onCreateContext(const ContextRec&, void* storage) const SK_OVERRIDE;
+    virtual bool onAsLuminanceColor(SkColor* lum) const SK_OVERRIDE {
+        *lum = fColor;
+        return true;
+    }
 
 private:
-    SkColor     fColor;         // ignored if fInheritColor is true
+    SkColor fColor;
 
     typedef SkShader INHERITED;
 };
 
 #endif