Cleanup dart to string conversions.

Source/WebCore/bindings/dart/custom/DartCanvasRenderingContext2DCustom.cpp

 // Copyright 2011, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
@@ skipping 79 matching lines @@
 
 void strokeStyleSetter(Dart_NativeArguments args)
 {
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
         CanvasRenderingContext2D* receiver = DartDOMWrapper::receiver<CanvasRenderingContext2D>(args);
 
         Dart_Handle arg = Dart_GetNativeArgument(args, 1);
         if (Dart_IsString(arg)) {
-            const ParameterAdapter<String> color(Dart_GetNativeArgument(args, 1));
-            if (!color.conversionSuccessful()) {
-                exception = color.exception();
+            DartStringAdapter color = DartUtilities::dartToString(Dart_GetNativeArgument(args, 1), exception);
+            if (exception)
                 goto fail;
-            }
 
             receiver->setStrokeColor(color);
             return;
         }
 
         receiver->setStrokeStyle(toCanvasStyle(arg));
         return;
     }
 
 fail:
@@ skipping 16 matching lines @@
 
 void fillStyleSetter(Dart_NativeArguments args)
 {
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
         CanvasRenderingContext2D* receiver = DartDOMWrapper::receiver<CanvasRenderingContext2D>(args);
 
         Dart_Handle arg = Dart_GetNativeArgument(args, 1);
         if (Dart_IsString(arg)) {
-            const ParameterAdapter<String> color(arg);
-            if (!color.conversionSuccessful()) {
-                exception = color.exception();
+            DartStringAdapter color = DartUtilities::dartToString(arg, exception);
+            if (exception)
                 goto fail;
-            }
 
             receiver->setFillColor(color);
             return;
         }
 
         receiver->setFillStyle(toCanvasStyle(arg));
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 } // namespace DartCanvasRenderingContext2DInternal
 
 } // namespace WebCore