[Extensions] Reduce string copy in renderer/ UserScript.

extensions/renderer/programmatic_script_injector.h

 // Copyright 2014 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 EXTENSIONS_RENDERER_PROGRAMMATIC_SCRIPT_INJECTOR_H_
 #define EXTENSIONS_RENDERER_PROGRAMMATIC_SCRIPT_INJECTOR_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 23 matching lines @@
   bool IsUserGesture() const override;
   bool ExpectsResults() const override;
   bool ShouldInjectJs(UserScript::RunLocation run_location) const override;
   bool ShouldInjectCss(UserScript::RunLocation run_location) const override;
   PermissionsData::AccessType CanExecuteOnFrame(
       const InjectionHost* injection_host,
       blink::WebLocalFrame* web_frame,
       int tab_id) const override;
   std::vector<blink::WebScriptSource> GetJsSources(
       UserScript::RunLocation run_location) const override;
-  std::vector<std::string> GetCssSources(
+  std::vector<blink::WebString> GetCssSources(
       UserScript::RunLocation run_location) const override;
   void GetRunInfo(ScriptsRunInfo* scripts_run_info,
                   UserScript::RunLocation run_location) const override;
   void OnInjectionComplete(std::unique_ptr<base::Value> execution_result,
                            UserScript::RunLocation run_location,
                            content::RenderFrame* render_frame) override;
   void OnWillNotInject(InjectFailureReason reason,
                        content::RenderFrame* render_frame) override;
 
   // Whether it is safe to include information about the URL in error messages.
@@ skipping 21 matching lines @@
 
   // Whether or not this script injection has finished.
   bool finished_;
 
   DISALLOW_COPY_AND_ASSIGN(ProgrammaticScriptInjector);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_PROGRAMMATIC_SCRIPT_INJECTOR_H_