exo: Fix event dispatch to frame view.

Use TARGET_AND_DESCENDANTS for event targeting policy to ensure
that frame view hit testing works correctly.

Bug: 836177
Test: window frame for xdg surfaces receive events in X11 cros build
Change-Id: I8a9cae6af24253c9611035353ea6120639f7b1c6
Reviewed-on: https://chromium-review.googlesource.com/1025633Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553120}

components/exo/shell_surface_base.cc

@@ -1204,7 +1204,7 @@ void ShellSurfaceBase::CreateShellSurfaceWidget(
   // The window of widget_ is a container window. It doesn't handle pointer
   // events.
   window->SetEventTargetingPolicy(
-      ui::mojom::EventTargetingPolicy::DESCENDANTS_ONLY);
+      ui::mojom::EventTargetingPolicy::TARGET_AND_DESCENDANTS);
   window->SetEventTargeter(base::WrapUnique(
       new CustomWindowTargeter(widget_, client_controlled_move_resize_)));
   SetApplicationId(window, application_id_);