Support choosing multiple files with fileSystem.chooseEntry.

chrome/test/data/extensions/api_test/file_system/save_multiple/test.js

Index: chrome/test/data/extensions/api_test/file_system/save_multiple/test.js
diff --git a/chrome/test/data/extensions/api_test/file_system/save_existing_with_write/test.js b/chrome/test/data/extensions/api_test/file_system/save_multiple/test.js
similarity index 55%
copy from chrome/test/data/extensions/api_test/file_system/save_existing_with_write/test.js
copy to chrome/test/data/extensions/api_test/file_system/save_multiple/test.js
index d987bbaf81b0205c63c615927ae275ee18c62084..fd3d65ed5d022a1cc552b9f43e272c772356208e 100644
--- a/chrome/test/data/extensions/api_test/file_system/save_existing_with_write/test.js
+++ b/chrome/test/data/extensions/api_test/file_system/save_multiple/test.js
@@ -4,9 +4,8 @@
 
 chrome.test.runTests([
   function saveFile() {
-    chrome.fileSystem.chooseEntry({type: 'saveFile'},
-        chrome.test.callbackPass(function(entry) {
-      checkEntry(entry, 'save_existing.txt', false, true);
-    }));
+    chrome.fileSystem.chooseEntry(
+        {type: 'saveFile', acceptsMultiple: true}, chrome.test.callbackFail(
+            "acceptsMultiple: true is not supported for 'saveFile'"));
   }
 ]);