[Extensions] Reduce string copy in renderer/ UserScript.

extensions/renderer/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_SCRIPT_INJECTOR_H_
 #define EXTENSIONS_RENDERER_SCRIPT_INJECTOR_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 51 matching lines @@
       blink::WebLocalFrame* web_frame,
       int tab_id) const = 0;
 
   // Returns the javascript sources to inject at the given |run_location|.
   // Only called if ShouldInjectJs() is true.
   virtual std::vector<blink::WebScriptSource> GetJsSources(
       UserScript::RunLocation run_location) const = 0;
 
   // Returns the css to inject at the given |run_location|.
   // Only called if ShouldInjectCss() is true.
-  virtual std::vector<std::string> GetCssSources(
+  virtual std::vector<blink::WebString> GetCssSources(
       UserScript::RunLocation run_location) const = 0;
 
   // Fill scriptrs run info based on information about injection.
   virtual void GetRunInfo(
       ScriptsRunInfo* scripts_run_info,
       UserScript::RunLocation run_location) const = 0;
 
   // Notifies the script that injection has completed, with a possibly-populated
   // list of results (depending on whether or not ExpectsResults() was true).
   // |render_frame| contains the render frame, or null if the frame was
   // invalidated.
   virtual void OnInjectionComplete(
       std::unique_ptr<base::Value> execution_result,
       UserScript::RunLocation run_location,
       content::RenderFrame* render_frame) = 0;
 
   // Notifies the script that injection will never occur.
   // |render_frame| contains the render frame, or null if the frame was
   // invalidated.
   virtual void OnWillNotInject(InjectFailureReason reason,
                                content::RenderFrame* render_frame) = 0;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_SCRIPT_INJECTOR_H_