Cleanup dart to string conversions.

Source/WebCore/bindings/dart/custom/DartHTMLCanvasElementCustom.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 38 matching lines @@
 
 namespace DartHTMLCanvasElementInternal {
 
 void toDataURLCallback(Dart_NativeArguments args)
 {
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
         HTMLCanvasElement* receiver = DartDOMWrapper::receiver<HTMLCanvasElement>(args);
 
-        const ParameterAdapter<String> type(Dart_GetNativeArgument(args, 1));
-        if (!type.conversionSuccessful()) {
-            exception = type.exception();
+        DartStringAdapter type = DartUtilities::dartToString(Dart_GetNativeArgument(args, 1), exception);
+        if (exception)
             goto fail;
-        }
 
         ExceptionCode ec = 0;
         String result = receiver->toDataURL(type, 0, ec);
         if (UNLIKELY(ec)) {
             exception = DartDOMWrapper::exceptionCodeToDartException(ec);
             goto fail;
         }
 
         Dart_SetReturnValue(args, DartUtilities::stringToDart(result, DartUtilities::ConvertNullToDefaultValue));
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 void getContextCallback(Dart_NativeArguments args)
 {
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
         HTMLCanvasElement* receiver = DartDOMWrapper::receiver<HTMLCanvasElement>(args);
 
-        const ParameterAdapter<String> contextId(Dart_GetNativeArgument(args, 1));
-        if (!contextId.conversionSuccessful()) {
-            exception = contextId.exception();
+        DartStringAdapter contextId = DartUtilities::dartToString(Dart_GetNativeArgument(args, 1), exception);
+        if (exception)
             goto fail;
-        }
 
         RefPtr<CanvasContextAttributes> attrs;
 #if ENABLE(WEBGL)
         const String& contextIdStr = contextId;
         if (contextIdStr == "experimental-webgl" || contextIdStr == "webkit-3d") {
             attrs = WebGLContextAttributes::create();
             // FIXME: IDL doesn't mention second argument, but JS
             // passes map with parameters describing desired context
             // features.
         }
@@ skipping 13 matching lines @@
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 } // namespace DartHTMLCanvasElementInternal
 
 } // namespace WebCore