Handle context menu opening via two finger gesture tap.

It is possible to open a context menu via two finger gesture tap. We
previously didn't handle this gesture so selection state was empty.

Bug: 1166274
Change-Id: I259082d7c41391a23ccabd99573343e77c68bc78
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627440Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#843216}

ash/system/holding_space/holding_space_item_view_delegate.cc

@@ -115,9 +115,10 @@ bool HoldingSpaceItemViewDelegate::OnHoldingSpaceItemViewAccessibleAction(
 void HoldingSpaceItemViewDelegate::OnHoldingSpaceItemViewGestureEvent(
     HoldingSpaceItemView* view,
     const ui::GestureEvent& event) {
-  // When a long press gesture occurs we are going to show the context menu.
-  // Ensure that the pressed `view` is the only view selected.
-  if (event.type() == ui::ET_GESTURE_LONG_PRESS) {
+  // When a long press or two finger tap gesture occurs we are going to show the
+  // context menu. Ensure that the pressed `view` is the only view selected.
+  if (event.type() == ui::ET_GESTURE_LONG_PRESS ||
+      event.type() == ui::ET_GESTURE_TWO_FINGER_TAP) {
     SetSelection(view);
     return;
   }