Entering overview mode with windows that are not tabbed browsers (e.g. File.App or a web app running in a window) fails and the visuals get stuck mid-animation -
 probably for the same reason (hitting the same NOTREACHED).

I have a draft at https://chromium-review.googlesource.com/c/617943 that seems to help.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5

commit a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5
Author: Valery Arkhangorodsky <varkha@chromium.org>
Date: Fri Aug 18 15:13:47 2017

Makes FilterOperation ALPHA_THRESHOLD and deps use a vector of Rects and not SkRegion

Changes the FilterOperation to keep a shape in a vector<gfx::Rect>.
Adds serialization support to cc.mojom.FilterOperation.
Plumbs new signatures through Widget, NativeWidget and WindowTreeHost
and ui::Layer.
Updates the OverviewMode (ScopedTransformOverviewWindow::HideHeader) to
use the new method of supplying alpha shape.

      2. Run chromeos Chrome with --mus,
         Open Files.App
         Press F5 to enter overview mode, should not get stuck

Bug:  754796 ,  754797 
Test: 1. browser_tests --gtest_filter=AppWindowApiTest.SetShapeHasPerm --mus
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Idb3dfd30c7e238a18d9c4ea8f2249c184d50258c
Reviewed-on: https://chromium-review.googlesource.com/617943
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Valery Arkhangorodsky <varkha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#495551}
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ash/wm/overview/scoped_transform_overview_window.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ash/wm/overview/scoped_transform_overview_window.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/base/filter_operation.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/base/filter_operation.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/base/render_surface_filters.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/ipc/cc_param_traits.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/ipc/filter_operation.mojom
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/ipc/filter_operation_struct_traits.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/cc/trees/layer_tree_host_pixeltest_filters.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/chrome/browser/ui/views/apps/chrome_native_app_window_views.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/compositor/layer.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/compositor/layer.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/compositor/layer_unittest.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/mus/desktop_window_tree_host_mus.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/mus/desktop_window_tree_host_mus.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_native_widget_aura.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_window_tree_host.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/desktop_window_tree_host_x11_unittest.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/desktop_aura/x11_topmost_window_finder_interactive_uitest.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/native_widget_aura.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/native_widget_aura.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/native_widget_mac.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/native_widget_mac.mm
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/native_widget_private.h
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/widget.cc
[modify] https://crrev.com/a5d3bb3f87f25745e4fa64c6d6cb0c63631ce3f5/ui/views/widget/widget.h