Cleanup dart to string conversions.

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

Index: Source/WebCore/bindings/dart/custom/DartHistoryCustom.cpp
diff --git a/Source/WebCore/bindings/dart/custom/DartHistoryCustom.cpp b/Source/WebCore/bindings/dart/custom/DartHistoryCustom.cpp
index d897a76965b2bbe7fd6af4f6acc3779b970a9325..82013b538e5c3245215bac32daf6f0e0ef66af8e 100644
--- a/Source/WebCore/bindings/dart/custom/DartHistoryCustom.cpp
+++ b/Source/WebCore/bindings/dart/custom/DartHistoryCustom.cpp
@@ -54,18 +54,14 @@ static void addStateObjectHelper(Dart_NativeArguments args, History::StateObject
         if (exception)
             goto fail;
 
-        const ParameterAdapter<String> title(Dart_GetNativeArgument(args, 2));
-        if (!title.conversionSuccessful()) {
-            exception = title.exception();
+        DartStringAdapter title = DartUtilities::dartToString(Dart_GetNativeArgument(args, 2), exception);
+        if (exception)
             goto fail;
-        }
 
         // FIXME: url argument should be optional.
-        const ParameterAdapter<String> url(Dart_GetNativeArgument(args, 3));
-        if (!url.conversionSuccessful()) {
-            exception = url.exception();
+        DartStringAdapter url = DartUtilities::dartToString(Dart_GetNativeArgument(args, 3), exception);
+        if (exception)
             goto fail;
-        }
 
         ExceptionCode ec = 0;
         receiver->stateObjectAdded(data.release(), title, url, stateObjectType, ec);