Decouple contrast boost from fake gamma.

src/core/SkScalerContext.h

 /*
  * Copyright 2006 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 SkScalerContext_DEFINED
 #define SkScalerContext_DEFINED
 
@@ skipping 53 matching lines @@
     }
     void setContrast(SkScalar c) {
         SkASSERT(0 <= c && c <= SK_Scalar1);
         fContrast = SkScalarRoundToInt(c * ((1 << 8) - 1));
     }
 
     /**
      *  Causes the luminance color and contrast to be ignored, and the
      *  paint and device gamma to be effectively 1.0.
      */
-    void ignorePreBlend() {
+    void ignorePreBlend(bool keepContrast) {
         setLuminanceColor(SK_ColorTRANSPARENT);
         setPaintGamma(SK_Scalar1);
         setDeviceGamma(SK_Scalar1);
-        setContrast(0);
+        if (!keepContrast) {
+            setContrast(0);
+        }
     }
 
     uint8_t     fMaskFormat;
     uint8_t     fStrokeJoin : 4;
     uint8_t     fStrokeCap : 4;
     uint16_t    fFlags;
     // Warning: when adding members note that the size of this structure
     // must be a multiple of 4. SkDescriptor requires that its arguments be
     // multiples of four and this structure is put in an SkDescriptor in
     // SkPaint::MakeRec.
@@ skipping 271 matching lines @@
     return static_cast<SkPaint::Hinting>(hint);
 }
 
 void SkScalerContextRec::setHinting(SkPaint::Hinting hinting) {
     fFlags = (fFlags & ~SkScalerContext::kHinting_Mask) |
                                 (hinting << SkScalerContext::kHinting_Shift);
 }
 
 
 #endif