Port more String and HashMap usages

sky/engine/tonic/dart_library_provider.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKY_ENGINE_TONIC_DART_LIBRARY_PROVIDER_H_
 #define SKY_ENGINE_TONIC_DART_LIBRARY_PROVIDER_H_
 
+#include <string>
+
 #include "base/callback.h"
 #include "dart/runtime/include/dart_api.h"
 #include "mojo/public/cpp/system/data_pipe.h"
-#include "sky/engine/wtf/text/WTFString.h"
 
 namespace blink {
 
 typedef base::Callback<void(mojo::ScopedDataPipeConsumerHandle)>
     DataPipeConsumerCallback;
 
 class DartLibraryProvider {
  public:
-  virtual void GetLibraryAsStream(const String& name,
+  virtual void GetLibraryAsStream(const std::string& name,
                                   DataPipeConsumerCallback callback) = 0;
 
   virtual Dart_Handle CanonicalizeURL(Dart_Handle library, Dart_Handle url) = 0;
 
   virtual ~DartLibraryProvider();
 };
 
 }  // namespace blink
 
 #endif  // SKY_ENGINE_TONIC_DART_LIBRARY_PROVIDER_H_