Prevent some string copies when sending Values to WebUI.

content/browser/webui/web_ui_impl.cc

 // 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.
 
 #include "content/browser/webui/web_ui_impl.h"
 
 #include <stddef.h>
 
 #include "base/debug/dump_without_crashing.h"
 #include "base/json/json_writer.h"
@@ skipping 37 matching lines @@
 
   WebUIImpl* web_ui_;
 };
 
 const WebUI::TypeID WebUI::kNoWebUI = NULL;
 
 // static
 base::string16 WebUI::GetJavascriptCall(
     const std::string& function_name,
     const std::vector<const base::Value*>& arg_list) {
-  base::string16 parameters;
+  base::string16 result(base::ASCIIToUTF16(function_name));
+  result.push_back('(');
+
   std::string json;
   for (size_t i = 0; i < arg_list.size(); ++i) {
     if (i > 0)
-      parameters += base::char16(',');
+      result.push_back(',');
 
     base::JSONWriter::Write(*arg_list[i], &json);
-    parameters += base::UTF8ToUTF16(json);
+    result.append(base::UTF8ToUTF16(json));
   }
-  return base::ASCIIToUTF16(function_name) +
-      base::char16('(') + parameters + base::char16(')') + base::char16(';');
+
+  result.push_back(')');
+  result.push_back(';');
+  return result;
 }
 
 WebUIImpl::WebUIImpl(WebContents* contents, const std::string& frame_name)
     : bindings_(BINDINGS_POLICY_WEB_UI),
       web_contents_(contents),
       web_contents_observer_(new MainFrameNavigationObserver(this, contents)),
       frame_name_(frame_name) {
   DCHECK(contents);
 }
 
@@ skipping 215 matching lines @@
   if (host->GetFrameName() == frame_name_)
     frame_set->insert(host);
 }
 
 void WebUIImpl::DisallowJavascriptOnAllHandlers() {
   for (const std::unique_ptr<WebUIMessageHandler>& handler : handlers_)
     handler->DisallowJavascript();
 }
 
 }  // namespace content