Hide tooltip when activating selection menu

Selecting a file, then tabbing to the selection menu button
should hide the tooltip if the menu is activated from the
keyboard. This change explicitly hides the tooltip on menu
activation.

      behaviour is correct on desktop and real device.

Bug: 752035
Test: Ran all FilesApp browser tests. Manually verified
Change-Id: I8c13364748773da2521129e95d7edb29c4032edd
Reviewed-on: https://chromium-review.googlesource.com/c/1347958Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610328}

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

@@ -34,6 +34,8 @@ function SelectionMenuController(selectionMenuButton, menu) {
 SelectionMenuController.prototype.onShowMenu_ = function() {
   this.menu_.classList.toggle('toolbar-menu', true);
   this.toggleRipple_.activated = true;
+  // crbug.com 752035 focus still on button, get rid of the tooltip
+  document.querySelector('files-tooltip').hideTooltip();
 };
 
 /**