Remove ComponentLoader's unnecessary string copy.

chrome/browser/extensions/component_loader.h

 // Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_COMPONENT_LOADER_H_
 #define CHROME_BROWSER_EXTENSIONS_COMPONENT_LOADER_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 37 matching lines @@
   // has been initialized, the extension is loaded; otherwise, the load is
   // deferred until LoadAll is called. The ID of the added extension is
   // returned.
   //
   // Component extension manifests must contain a "key" property with a unique
   // public key, serialized in base64. You can create a suitable value with the
   // following commands on a unixy system:
   //
   //   ssh-keygen -t rsa -b 1024 -N '' -f /tmp/key.pem
   //   openssl rsa -pubout -outform DER < /tmp/key.pem 2>/dev/null | base64 -w 0
-  std::string Add(const std::string& manifest_contents,
+  std::string Add(const base::StringPiece& manifest_contents,
                   const base::FilePath& root_directory);
 
   // Convenience method for registering a component extension by resource id.
   std::string Add(int manifest_resource_id,
                   const base::FilePath& root_directory);
 
   // Loads a component extension from file system. Replaces previously added
   // extension with the same ID.
   std::string AddOrReplace(const base::FilePath& path);
 
@@ skipping 57 matching lines @@
 
     // The component extension's ID.
     std::string extension_id;
   };
 
   // Parses the given JSON manifest. Returns nullptr if it cannot be parsed or
   // if the result is not a DictionaryValue.
   base::DictionaryValue* ParseManifest(
       base::StringPiece manifest_contents) const;
 
-  std::string Add(const std::string& manifest_contents,
+  std::string Add(const base::StringPiece& manifest_contents,
                   const base::FilePath& root_directory,
                   bool skip_whitelist);
   std::string Add(const base::DictionaryValue* parsed_manifest,
                   const base::FilePath& root_directory,
                   bool skip_whitelist);
 
   // Loads a registered component extension.
   void Load(const ComponentExtensionInfo& info);
 
   void AddDefaultComponentExtensionsWithBackgroundPages(
@@ skipping 61 matching lines @@
   base::WeakPtrFactory<ComponentLoader> weak_factory_;
 
   friend class TtsApiTest;
 
   DISALLOW_COPY_AND_ASSIGN(ComponentLoader);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_COMPONENT_LOADER_H_