Remove SK_SUPPORT_LEGACY_GRADIENT_DITHERING from Skia proper

gm/shallowgradient.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkGradientShader.h"
 
@@ skipping 19 matching lines @@
                                                    SkShader::kClamp_TileMode);
 }
 
 static SkShader* shader_sweep(const SkColor colors[], int count, const SkSize& size) {
     return SkGradientShader::CreateSweep(size.width()/2, size.height()/2,
                                          colors, nullptr, count);
 }
 
 class ShallowGradientGM : public skiagm::GM {
 public:
-    ShallowGradientGM(MakeShaderProc proc, const char name[]) : fProc(proc) {
+    ShallowGradientGM(MakeShaderProc proc, const char name[], bool dither)
+        : fProc(proc)
+        , fDither(dither) {
         fName.printf("shallow_gradient_%s", name);
     }
 
 protected:
 
     SkString onShortName() override {
         return fName;
     }
 
     SkISize onISize() override {
         return SkISize::Make(800, 800);
     }
 
     void onDraw(SkCanvas* canvas) override {
         const SkColor colors[] = { sk_tool_utils::color_to_565(0xFF555555), 
                 sk_tool_utils::color_to_565(0xFF444444) };
         const int colorCount = SK_ARRAY_COUNT(colors);
 
         SkRect r = { 0, 0, this->width(), this->height() };
         SkSize size = SkSize::Make(r.width(), r.height());
 
         SkPaint paint;
         paint.setShader(fProc(colors, colorCount, size))->unref();
+        paint.setDither(fDither);
         canvas->drawRect(r, paint);
     }
 
 private:
     MakeShaderProc fProc;
     SkString fName;
+    bool fDither;
 
     typedef skiagm::GM INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
-DEF_GM( return new ShallowGradientGM(shader_linear, "linear"); )
-DEF_GM( return new ShallowGradientGM(shader_radial, "radial"); )
-DEF_GM( return new ShallowGradientGM(shader_conical, "conical"); )
-DEF_GM( return new ShallowGradientGM(shader_sweep, "sweep"); )
+DEF_GM( return new ShallowGradientGM(shader_linear, "linear", true); )
+DEF_GM( return new ShallowGradientGM(shader_radial, "radial", true); )
+DEF_GM( return new ShallowGradientGM(shader_conical, "conical", true); )
+DEF_GM( return new ShallowGradientGM(shader_sweep, "sweep", true); )
+
+DEF_GM( return new ShallowGradientGM(shader_linear, "linear_nodither", false); )
+DEF_GM( return new ShallowGradientGM(shader_radial, "radial_nodither", false); )
+DEF_GM( return new ShallowGradientGM(shader_conical, "conical_nodither", false); )
+DEF_GM( return new ShallowGradientGM(shader_sweep, "sweep_nodither", false); )