Update references to the extension messaging APIs to point to the "runtime"

chrome/test/data/extensions/api_test/filesystem_handler_write/tab.js

 // 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.
 
 /*
 This extension is a file intent handler and does the following during the test:
 
 1. It first registers content hander.
 2. When content handler callback is invoked, opens tab.html page and passes
    file url via hash ref.
@@ skipping 25 matching lines @@
         break;
       case FileError.INVALID_STATE_ERR:
         msg = 'INVALID_STATE_ERR';
         break;
       default:
         msg = 'Unknown Error';
         break;
     };
   }
 
-  chrome.extension.sendMessage(fileBrowserExtensionId,
+  chrome.runtime.sendMessage(fileBrowserExtensionId,
                                {fileContent: null,
                                 error: {message: "File handler error: " + msg}},
                                 function(response) {});
 };
 
 function onSuccess(text) {
-  chrome.extension.sendMessage(
+  chrome.runtime.sendMessage(
       fileBrowserExtensionId,
       {fileContent: text, error: null},
       function(response) {});
 };
 
 function writeToFile(entry, text) {
   console.log('create writer');
   entry.createWriter(function(writer) {
     writer.onerror = function(e) {
       errorCallback(writer.error);
     };
     writer.onwrite = onSuccess.bind(this, text);
 
     var blob = new Blob([text + text], {type: 'text/plain'});
     writer.write(blob);
   });
 };
 
 function runFileSystemHandlerTest(entries) {
   if (!entries || entries.length != 1 || !entries[0]) {
-    chrome.extension.sendMessage(
+    chrome.runtime.sendMessage(
         fileBrowserExtensionId,
         {fileContent: null, error: 'Invalid file entries.'},
         function(response) {});
     return;
   }
   var entry = entries[0];
   var reader = new FileReader();
   reader.onloadend = function(e) {
     writeToFile(entry, reader.result);
   };
@@ skipping 30 matching lines @@
 // This extension just initializes its chrome.fileBrowserHandler.onExecute
 // event listener, the real testing is done when this extension's handler is
 // invoked from filebrowser_component tests. This event will be raised from that
 // component extension test and it simulates user action in the file browser.
 // tab.html part of this extension can run only after the component raises this
 // event, since that operation sets the propery security context and creates
 // event's payload with proper file Entry instances. tab.html will return
 // results of its execution to filebrowser_component test through a
 // cross-component message.
 chrome.test.succeed();