Before we make serializing SkRegion work we should make sure we actually need the richness of SkRegion. We need to look at all uses of SetShape() and verify they really need an SkRegion. It looks like the chrome app api triggerling this (AppWindow.SetShape()) is an array of rects.
Valery mentions another place hitting this DCHECK. See his comment in 754796.

Yes, same draft at https://chromium-review.googlesource.com/c/617943 should deal with this.

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