[MD] replace infobar bottom solid line separator with a shadow.

ui/gfx/skia_util.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/skia_util.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/numerics/safe_conversions.h"
@@ skipping 112 matching lines @@
 skia::RefPtr<SkShader> CreateGradientShader(int start_point,
                                             int end_point,
                                             SkColor start_color,
                                             SkColor end_color) {
   SkColor grad_colors[2] = { start_color, end_color};
   SkPoint grad_points[2];
   grad_points[0].iset(0, start_point);
   grad_points[1].iset(0, end_point);
 
   return skia::AdoptRef(SkGradientShader::CreateLinear(
-      grad_points, grad_colors, NULL, 2, SkShader::kRepeat_TileMode));
+      grad_points, grad_colors, NULL, 2, SkShader::kClamp_TileMode));

[sky, 2016/03/16 15:39:42]

Why does this change matter?

[Evan Stade, 2016/03/16 19:29:52]

ASCII art of what we want is something like:

---------------------
black 10%
black 10%
black 10%
black 10%
black 8%
black 6%
black 4%
black 2%
black 0%
---------------------

So we define the middle gradient point and the final gradient point. Clamp means
the black 10% is then repeated all the way to the top edge. With tile, this
would end up looking something like

---------------------
black 4%
black 2%
black 0%
black 10%
black 8%
black 6%
black 4%
black 2%
black 0%
---------------------

[sky, 2016/03/16 21:56:55]

Are you sure other call sites don't want the current behavior?

 }
 
 static SkScalar RadiusToSigma(double radius) {
   // This captures historically what skia did under the hood. Now skia accepts
   // sigma, not radius, so we perform the conversion.
   return radius > 0 ? SkDoubleToScalar(0.57735f * radius + 0.5) : 0;
 }
 
 skia::RefPtr<SkDrawLooper> CreateShadowDrawLooper(
     const std::vector<ShadowValue>& shadows) {
@@ skipping 94 matching lines @@
   static const SkScalar kSkToHbRatio = SK_Scalar1 / kHbUnit1;
   return kSkToHbRatio * value;
 }
 
 float HarfBuzzUnitsToFloat(int value) {
   static const float kFloatToHbRatio = 1.0f / kHbUnit1;
   return kFloatToHbRatio * value;
 }
 
 }  // namespace gfx