Fix closure compililation error in Files.app.

TBR=yawano@chromium.org
BUG=none
TEST=TEST=GYP_GENERATORS=ninja gyp --depth . ui/file_manager/file_manager/foreground/js/compiled_resources.gyp && ninja -C out/Default

Review URL: https://codereview.chromium.org/909883002

Cr-Commit-Position: refs/heads/master@{#315315}

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

@@ -95,6 +95,7 @@ ToolbarController.prototype.onCancelSelectionButtonClicked_ = function() {
  */
 ToolbarController.prototype.onNavigationListRelayout_ = function() {
   // Make the width of spacer same as the width of navigation list.
-  var navWidth = parseFloat(getComputedStyle(this.navigationList_).width);
+  var navWidth = parseFloat(
+      window.getComputedStyle(this.navigationList_).width);
   this.cancelSelectionButtonWrapper_.style.width = navWidth + 'px';
 }