Cleanup dart to string conversions.

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

Index: Source/WebCore/bindings/dart/custom/DartWebKitCSSMatrixCustom.cpp
diff --git a/Source/WebCore/bindings/dart/custom/DartWebKitCSSMatrixCustom.cpp b/Source/WebCore/bindings/dart/custom/DartWebKitCSSMatrixCustom.cpp
index d63af1b3b859527ce7abbe0a473a460c2a0231aa..338e95a79e033cfdc1570fd03626a792bc1fe7a8 100644
--- a/Source/WebCore/bindings/dart/custom/DartWebKitCSSMatrixCustom.cpp
+++ b/Source/WebCore/bindings/dart/custom/DartWebKitCSSMatrixCustom.cpp
@@ -44,11 +44,9 @@ void constructorCallback(Dart_NativeArguments args)
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
-        const ParameterAdapter<String> cssValue(Dart_GetNativeArgument(args, 0), DartUtilities::ConvertNullToDefaultValue);
-        if (!cssValue.conversionSuccessful()) {
-            exception = cssValue.exception();
+        DartStringAdapter cssValue = DartUtilities::dartToStringWithNullCheck(Dart_GetNativeArgument(args, 0), exception);
+        if (exception)
             goto fail;
-        }
 
         ExceptionCode ec = 0;
         RefPtr<WebKitCSSMatrix> matrix = WebKitCSSMatrix::create(cssValue, ec);