Cleanup dart to string conversions.

Source/WebCore/bindings/dart/custom/DartWebGLRenderingContextCustom.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 246 matching lines @@
 {
     getObjectParameter(args, kBuffer);
 }
 
 void getExtensionCallback(Dart_NativeArguments args)
 {
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
         WebGLRenderingContext* context = DartDOMWrapper::receiver<WebGLRenderingContext>(args);
-        const ParameterAdapter<String> name(Dart_GetNativeArgument(args, 1));
-        if (!name.conversionSuccessful()) {
-            exception = name.exception();
+        DartStringAdapter name = DartUtilities::dartToString(Dart_GetNativeArgument(args, 1), exception);
+        if (exception)
             goto fail;
-        }
 
         WebGLExtension* extension = context->getExtension(name);
         Dart_Handle result = webGLExtensionToDart(extension);
         if (!DartUtilities::checkResult(result, exception))
             goto fail;
         Dart_SetReturnValue(args, result);
         return;
     }
 
 fail:
@@ skipping 449 matching lines @@
 void vertexAttrib4fvCallback(Dart_NativeArguments args)
 {
     vertexAttribAndUniformHelperf(args, kVertexAttrib4v);
 }
 
 }
 
 }
 
 #endif // ENABLE(WEBGL)