Port more String and HashMap usages

sky/shell/dart/dart_library_provider_files.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_SHELL_DART_DART_LIBRARY_PROVIDER_FILES_H_
 #define SKY_SHELL_DART_DART_LIBRARY_PROVIDER_FILES_H_
 
 #include "base/files/file_path.h"
 #include "sky/engine/tonic/dart_library_provider.h"
 
 namespace sky {
 namespace shell {
 
 class DartLibraryProviderFiles : public blink::DartLibraryProvider {
  public:
   explicit DartLibraryProviderFiles(const base::FilePath& package_root);
   ~DartLibraryProviderFiles() override;
 
  protected:
   // |DartLibraryProvider| implementation:
-  void GetLibraryAsStream(const String& name,
+  void GetLibraryAsStream(const std::string& name,
                           blink::DataPipeConsumerCallback callback) override;
   Dart_Handle CanonicalizeURL(Dart_Handle library, Dart_Handle url) override;
 
  private:
   std::string CanonicalizePackageURL(std::string url);
 
   base::FilePath package_root_;
 
   DISALLOW_COPY_AND_ASSIGN(DartLibraryProviderFiles);
 };
 
 }  // namespace shell
 }  // namespace sky
 
 #endif  // SKY_SHELL_DART_DART_LIBRARY_PROVIDER_FILES_H_