Gallery: Disable name input when the selection is empty.

BUG=405820
TEST=manually

Review URL: https://codereview.chromium.org/490113002

Cr-Commit-Position: refs/heads/master@{#291020}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@291020 0039d316-1c4b-4281-b951-d872f2087c98

ui/file_manager/gallery/js/gallery.js

@@ -870,6 +870,7 @@ Gallery.prototype.updateSelectionAndState_ = function() {
     }
   } else {
     document.title = '';
+    this.filenameEdit_.disabled = true;
     this.filenameEdit_.value = '';
     this.shareButton_.hidden = true;
   }