Only use fake gamma with linear devices.

include/core/SkPaint.h

Index: include/core/SkPaint.h
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index cd170bc94f9f8fb209305e1232c1cfd449554ed9..482483f43a9f99677b2682af8d0ba0d61105a181 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -1072,19 +1072,24 @@ private:
     SkScalar measure_text(SkGlyphCache*, const char* text, size_t length,
                           int* count, SkRect* bounds) const;
 
+    enum class FakeGamma {
+        Off = 0, On
+    };
+
     /*
      * Allocs an SkDescriptor on the heap and return it to the caller as a refcnted
      * SkData.  Caller is responsible for managing the lifetime of this object.
      */
     void getScalerContextDescriptor(SkAutoDescriptor*, const SkSurfaceProps& surfaceProps,
-                                    const SkMatrix*, bool ignoreGamma) const;
+                                    FakeGamma fakeGamma, const SkMatrix*) const;
 
-    SkGlyphCache* detachCache(const SkSurfaceProps* surfaceProps, const SkMatrix*,
-                              bool ignoreGamma) const;
+    SkGlyphCache* detachCache(const SkSurfaceProps* surfaceProps, FakeGamma fakeGamma,
+                              const SkMatrix*) const;
 
-    void descriptorProc(const SkSurfaceProps* surfaceProps, const SkMatrix* deviceMatrix,
+    void descriptorProc(const SkSurfaceProps* surfaceProps, FakeGamma fakeGamma,
+                        const SkMatrix* deviceMatrix,
                         void (*proc)(SkTypeface*, const SkDescriptor*, void*),
-                        void* context, bool ignoreGamma) const;
+                        void* context) const;
 
     /*
      * The luminance color is used to determine which Gamma Canonical color to map to.  This is