Update directory tree's scrollbar when the progress center mutates.

ui/file_manager/file_manager/foreground/js/file_manager.js

Index: ui/file_manager/file_manager/foreground/js/file_manager.js
diff --git a/ui/file_manager/file_manager/foreground/js/file_manager.js b/ui/file_manager/file_manager/foreground/js/file_manager.js
index 3ac1db6e7c3c915c9d45f9c9fb964f409bf47289..c2452c11423ce76af04321622c682aa8c0aab539 100644
--- a/ui/file_manager/file_manager/foreground/js/file_manager.js
+++ b/ui/file_manager/file_manager/foreground/js/file_manager.js
@@ -1045,6 +1045,14 @@ var BOTTOM_MARGIN_FOR_PREVIEW_PANEL_PX = 52;
                            fakeEntriesVisible);
     this.directoryTree_.dataModel = new NavigationListModel(
         this.volumeManager_, this.folderShortcutsModel_);
+
+    // Visible height of the directory tree depends on the size of progress
+    // center panel. When the size of progress center panel changes, directory
+    // tree has to be notified to adjust its components (e.g. progress bar).
+    var observer = new MutationObserver(
+        this.directoryTree_.relayout.bind(this.directoryTree_));
+    observer.observe(this.progressCenterPanel_.element,
+                     {subtree: true, attributes: true, childList: true});
   };
 
   /**