Fix Mosaic view button in the Photo Editor

BUG=169239

Review URL: https://codereview.chromium.org/11824060

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176070 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/file_manager/js/photo/gallery.js

@@ -244,7 +244,7 @@ Gallery.prototype.initDom_ = function() {
   var onThumbnailError = this.context_.onThumbnailError || function() {};
 
   if (this.context_.allowMosaic) {
-    this.modeButton_ = util.createChild(this.toolbar_, 'button mode');
+    this.modeButton_ = util.createChild(this.toolbar_, 'button mode', 'button');
     this.modeButton_.addEventListener('click',
         this.toggleMode_.bind(this, null));