Dispatch directory-changed event before rescan starts.

Directory rescan sometimes uses up IO and blocks other IOs which are necessary
for updating the top-left breadcrumb. While this CL does not solve the real
cause of the issue, this CL mitigates the problem by dispatching event earlier.

BUG=459864
TEST=manually tested as described in the issue

Review URL: https://codereview.chromium.org/943473002

Cr-Commit-Position: refs/heads/master@{#317021}

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

@@ -919,6 +919,18 @@ DirectoryModel.prototype.changeDirectoryEntry = function(
 
           var previousDirEntry =
               this.currentDirContents_.getDirectoryEntry();
+          var previousVolumeInfo =
+              previousDirEntry ?
+              this.volumeManager_.getVolumeInfo(previousDirEntry) : null;
+
+          // VolumeInfo for dirEntry.
+          var currentVolumeInfo = this.getCurrentVolumeInfo();
+          var event = new Event('directory-changed');
+          event.previousDirEntry = previousDirEntry;
+          event.newDirEntry = dirEntry;
+          event.volumeChanged = previousVolumeInfo !== currentVolumeInfo;
+          this.dispatchEvent(event);
+
           this.clearAndScan_(
               newDirectoryContents,
               function(result) {
@@ -934,16 +946,6 @@ DirectoryModel.prototype.changeDirectoryEntry = function(
           // For tests that open the dialog to empty directories, everything
           // is loaded at this point.
           util.testSendMessage('directory-change-complete');
-          var previousVolumeInfo =
-              previousDirEntry ?
-              this.volumeManager_.getVolumeInfo(previousDirEntry) : null;
-          // VolumeInfo for dirEntry.
-          var currentVolumeInfo = this.getCurrentVolumeInfo();
-          var event = new Event('directory-changed');
-          event.previousDirEntry = previousDirEntry;
-          event.newDirEntry = dirEntry;
-          event.volumeChanged = previousVolumeInfo !== currentVolumeInfo;
-          this.dispatchEvent(event);
         }.bind(this));
   }.bind(this, this.changeDirectorySequence_));
 };