Gallery: Add debugMe method to Gallery.

ui/file_manager/gallery/js/mosaic_mode_unittest.js

+// Copyright 2015 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.
+
+// Mocking load detached image function.
+ThumbnailLoader.prototype.loadDetachedImage = function(call) {
+  call(true);
+};
+
+function testBasic() {
+  var fileSystem = new MockFileSystem('volumeId');
+  var entry = new MockEntry(fileSystem, '/test.jpg');
+  var item = new Gallery.Item(entry, {}, {}, {}, true);
+  var model = new cr.ui.ArrayDataModel([item]);
+  var selection = new cr.ui.ListSelectionModel();
+  var mosaic = new Mosaic(
+      document, null, model, selection, {getLocationInfo: function() {}});
+  document.documentElement.appendChild(mosaic);
+  mosaic.init();
+  mosaic.layout();
+  assertEquals(1, mosaic.querySelectorAll('.mosaic-tile').length);
+  assertEquals(1, mosaic.querySelectorAll(
+      '.mosaic-tile .load-target-file-entry').length);
+}