drive: Make FileManagerBrowserTest more robust

chrome/test/data/extensions/api_test/file_manager_browsertest/background.js

Index: chrome/test/data/extensions/api_test/file_manager_browsertest/background.js
diff --git a/chrome/test/data/extensions/api_test/file_manager_browsertest/background.js b/chrome/test/data/extensions/api_test/file_manager_browsertest/background.js
index 6e5c689844b980b08423e465b868a7ef1f634c71..704d33a4c59c971c291b22f7c16d9201b4663345 100644
--- a/chrome/test/data/extensions/api_test/file_manager_browsertest/background.js
+++ b/chrome/test/data/extensions/api_test/file_manager_browsertest/background.js
@@ -84,17 +84,19 @@ function waitAndAcceptDialog(callback) {
 // Checks that the files initially added by the C++ side are displayed, and
 // that a subsequently added file shows up.
 function testFileDisplay() {
-  getFileList(function(actualFilesBefore) {
-    chrome.test.assertEq(EXPECTED_FILES_BEFORE, actualFilesBefore);
-    chrome.test.sendMessage('initial check done', function(reply) {
-      chrome.test.assertEq('file added', reply);
-      waitForFileListChange(
+  waitForFileListChange(
+    0,
+    function(actualFilesBefore) {
+      chrome.test.assertEq(EXPECTED_FILES_BEFORE, actualFilesBefore);
+      chrome.test.sendMessage('initial check done', function(reply) {
+        chrome.test.assertEq('file added', reply);
+        waitForFileListChange(
           EXPECTED_FILES_BEFORE.length,
           chrome.test.callbackPass(function(actualFilesAfter) {
             chrome.test.assertEq(EXPECTED_FILES_AFTER, actualFilesAfter);
           }));
+      });
     });
-  });
 }
 
 // Injects the keyboard test code into the file manager tab and runs the