Reject filesystem root entries as args for chrome.fileSystem functions.

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

Index: chrome/test/data/extensions/api_test/file_system/get_writable_root_entry/test.js
diff --git a/chrome/test/data/extensions/api_test/file_system/get_writable_file_entry_with_write/test.js b/chrome/test/data/extensions/api_test/file_system/get_writable_root_entry/test.js
similarity index 61%
copy from chrome/test/data/extensions/api_test/file_system/get_writable_file_entry_with_write/test.js
copy to chrome/test/data/extensions/api_test/file_system/get_writable_root_entry/test.js
index 08ff1e531163b577bc30f01a3fdabe32f8476592..205bf9c8f6242ebcbd9c6b55d516e2764b17143b 100644
--- a/chrome/test/data/extensions/api_test/file_system/get_writable_file_entry_with_write/test.js
+++ b/chrome/test/data/extensions/api_test/file_system/get_writable_root_entry/test.js
@@ -6,11 +6,10 @@ chrome.test.runTests([
   function getWritableEntry() {
     chrome.fileSystem.chooseEntry(chrome.test.callbackPass(function(entry) {
       chrome.test.assertEq('writable.txt', entry.name);
-      // Test that we can get the display path of the file.
-      chrome.fileSystem.getWritableEntry(entry, chrome.test.callbackPass(
-          function(writable) {
-        checkEntry(writable, 'writable.txt', false, true);
-      }));
+      // Test that we cannot get a writable entry for the root entry.
+      chrome.fileSystem.getWritableEntry(
+          entry.filesystem.root, chrome.test.callbackFail(
+              'Invalid parameters'));
     }));
   }
 ]);