Add support for linear gradients, implemented as skia shaders.

sky/engine/core/painting/Point.cpp

 // 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/Point.h"
 
 #include "sky/engine/core/script/dom_dart_state.h"
 #include "sky/engine/tonic/dart_error.h"
 #include "base/logging.h"
 
 namespace blink {
 
-// Convert dartPoint.x,y ==> SkPoint.
-Point DartConverter<Point>::FromArgumentsWithNullCheck(
-    Dart_NativeArguments args,
-    int index,
-    Dart_Handle& exception) {
+// Convert handle.x,y ==> SkPoint.
+Point DartConverter<Point>::FromDart(Dart_Handle handle) {
   Point result;
   result.is_null = true;
 
-  Dart_Handle dartPoint = Dart_GetNativeArgument(args, index);
-  DCHECK(!LogIfError(dartPoint));
+  DCHECK(!LogIfError(handle));
 
   Dart_Handle x_value =
-      Dart_GetField(dartPoint, DOMDartState::Current()->x_handle());
+      Dart_GetField(handle, DOMDartState::Current()->x_handle());
   Dart_Handle y_value =
-      Dart_GetField(dartPoint, DOMDartState::Current()->y_handle());
+      Dart_GetField(handle, DOMDartState::Current()->y_handle());
 
   double x = 0.0, y = 0.0;
   Dart_Handle err = Dart_DoubleValue(x_value, &x);
   DCHECK(!LogIfError(err));
   err = Dart_DoubleValue(y_value, &y);
   DCHECK(!LogIfError(err));
   result.sk_point.set(x, y);
   result.is_null = false;
   return result;
 }
 
+Point DartConverter<Point>::FromArgumentsWithNullCheck(
+    Dart_NativeArguments args,
+    int index,
+    Dart_Handle& exception) {
+  return FromDart(Dart_GetNativeArgument(args, index));
+}
+
 } // namespace blink