Add support for drive files to chrome.fileBrowserHandler.selectFile

chrome/test/data/extensions/api_test/file_browser/filehandler_create/test.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.
 
 var EXTENSION_ID = 'kidcpjlbjdmcnmccjhjdckhbngnhnepk';
 var FILE_CONTENTS = 'hello from test extension.';
 
 function errorCallback(error) {
   var msg = '';
   if (!error.code) {
@@ skipping 17 matching lines @@
         break;
       default:
         msg = 'Unknown Error';
         break;
     };
   }
   console.log(msg);
   chrome.test.fail(msg);
 }
 
+function ensureFileExists(entry, successCallback, errorCallback) {
+  entry.filesystem.root.getFile(entry.fullPath,
+                                {create: true},
+                                successCallback,
+                                errorCallback);
+}
+
 function writeToFile(entry) {
   entry.createWriter(function(writer) {
     writer.onerror = function(e) {
       errorCallback(writer.error);
     };
     writer.onwrite = chrome.test.succeed;
 
     var bb = new WebKitBlobBuilder();
     bb.append(FILE_CONTENTS);
     writer.write(bb.getBlob('text/plain'));
   }, errorCallback);
 }
 
 chrome.test.runTests([
   function selectionSuccessful() {
     // The test will call selectFile function and expect it to succeed.
     // When it gets the file entry, it verifies that the permissions given in
     // the method allow the extension to read/write to selected file.
     chrome.fileBrowserHandler.selectFile({ suggestedName: 'some_file_name.txt'},
         function(result) {
           chrome.test.assertTrue(!!result);
           chrome.test.assertTrue(result.success);
           chrome.test.assertTrue(!!result.entry);
 
-         writeToFile(result.entry);
+         ensureFileExists(result.entry, writeToFile, errorCallback);
       });
   },
   function selectionFails() {
     // The test expects that selectFile returns failure with an empty entry.
     chrome.fileBrowserHandler.selectFile({ suggestedName: 'fail' },
         function(result) {
           chrome.test.assertTrue(!!result);
           // Entry should be set iff operation succeeded.
           chrome.test.assertEq(false, result.success);
           chrome.test.assertTrue(result.entry == null);
           chrome.test.succeed();
         });
   }]);