Cleanup dart to string conversions.

Source/WebCore/bindings/dart/custom/DartHTMLInputElementCustom.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 36 matching lines @@
         }
 
         int start = DartUtilities::dartToInt(Dart_GetNativeArgument(args, 1), exception);
         if (exception)
             goto fail;
 
         int end = DartUtilities::dartToInt(Dart_GetNativeArgument(args, 2), exception);
         if (exception)
             goto fail;
 
-        const ParameterAdapter<String> direction(Dart_GetNativeArgument(args, 3));
-        if (!direction.conversionSuccessful()) {
-            exception = direction.exception();
+        DartStringAdapter direction = DartUtilities::dartToString(Dart_GetNativeArgument(args, 3), exception);
+        if (exception)
             goto fail;
-        }
 
         receiver->setSelectionRange(start, end, direction);
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
@@ skipping 23 matching lines @@
     DartApiScope dartApiScope;
     Dart_Handle exception = 0;
     {
         HTMLInputElement* receiver = DartDOMWrapper::receiver<HTMLInputElement>(args);
 
         if (!receiver->canHaveSelection()) {
             exception = Dart_NewString("Accessing selectionDirection on an input element that cannot have a selection.");
             goto fail;
         }
 
-        const ParameterAdapter<String> value(Dart_GetNativeArgument(args, 1));
-        if (!value.conversionSuccessful()) {
-            exception = value.exception();
+        DartStringAdapter value = DartUtilities::dartToString(Dart_GetNativeArgument(args, 1), exception);
+        if (exception)
             goto fail;
-        }
 
         receiver->setSelectionDirection(value);
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
@@ skipping 85 matching lines @@
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 }
 
 }