Add support for linear gradients, implemented as skia shaders.

sky/engine/core/painting/CanvasGradient.cpp

Index: sky/engine/core/painting/CanvasGradient.cpp
diff --git a/sky/engine/core/painting/CanvasGradient.cpp b/sky/engine/core/painting/CanvasGradient.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..5e356ef03b0820c8b9dd2e0f4508698e824622ed
--- /dev/null
+++ b/sky/engine/core/painting/CanvasGradient.cpp
@@ -0,0 +1,40 @@
+// Copyright 2015 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 "sky/engine/config.h"
+#include "sky/engine/core/painting/CanvasGradient.h"
+
+#include "base/logging.h"
+#include "sky/engine/core/painting/Picture.h"
+
+namespace blink {
+
+PassRefPtr<CanvasGradient> CanvasGradient::create(
+    int type,
+    const Vector<Point>& end_points,
+    const Vector<SkColor>& colors,
+    const Vector<float>& color_stops) {
+  ASSERT(type == 0);  // Only 1 supported type so far.
+  ASSERT(end_points.size() == 2);
+  ASSERT(colors.size() == color_stops.size() || color_stops.data() == nullptr);
+  SkPoint sk_end_points[2];
+  for (int i = 0; i < 2; ++i)
+    sk_end_points[i] = end_points[i].sk_point;
+
+  SkShader* shader = SkGradientShader::CreateLinear(
+      sk_end_points, colors.data(), color_stops.data(), colors.size(),
+      SkShader::kClamp_TileMode);
+  return adoptRef(new CanvasGradient(adoptRef(shader)));
+}
+
+CanvasGradient::CanvasGradient(PassRefPtr<SkShader> shader)
+    : Shader(shader)
+{
+}
+
+CanvasGradient::~CanvasGradient()
+{
+}
+
+} // namespace blink