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

include/core/SkColorShader.h

Index: include/core/SkColorShader.h
diff --git a/include/core/SkColorShader.h b/include/core/SkColorShader.h
index 4ff7d2b01d375b64659c1db2a81e3e59bb4c84d7..55d980b64e38909e4122645fd622c5713f7b8a73 100644
--- a/include/core/SkColorShader.h
+++ b/include/core/SkColorShader.h
@@ -1,4 +1,3 @@
-
 /*
  * Copyright 2007 The Android Open Source Project
  *
@@ -6,7 +5,6 @@
  * found in the LICENSE file.
  */
 
-
 #ifndef SkColorShader_DEFINED
 #define SkColorShader_DEFINED
 
@@ -67,9 +65,13 @@ 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;
 };