Add unit tests for drive::FileTaskExecutor.

chrome/browser/drive/fake_drive_service.cc

Index: chrome/browser/drive/fake_drive_service.cc
diff --git a/chrome/browser/drive/fake_drive_service.cc b/chrome/browser/drive/fake_drive_service.cc
index c69b2166b03cba0d4fc8678dc558c3d741ceae42..ae9cfecc48bf21aac25c0a2f91339aa645c5de34 100644
--- a/chrome/browser/drive/fake_drive_service.cc
+++ b/chrome/browser/drive/fake_drive_service.cc
@@ -1168,6 +1168,16 @@ CancelCallback FakeDriveService::AuthorizeApp(
     const AuthorizeAppCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(!callback.is_null());
+
+  if (entries_.count(resource_id) == 0) {
+    callback.Run(google_apis::HTTP_NOT_FOUND, GURL());
+    return CancelCallback();
+  }
+
+  callback.Run(HTTP_SUCCESS,
+               GURL(base::StringPrintf(open_url_format_.c_str(),
+                                       resource_id.c_str(),
+                                       app_id.c_str())));
   return CancelCallback();
 }