mus: Add debug key to print the server window hierarchy

components/mus/public/interfaces/window_manager.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mus.mojom;
 
 import "components/mus/public/interfaces/event_matcher.mojom";
 import "components/mus/public/interfaces/input_events.mojom";
 import "components/mus/public/interfaces/window_manager_constants.mojom";
 import "ui/mojo/geometry/geometry.mojom";
@@ skipping 63 matching lines @@
   SetUnderlaySurfaceOffsetAndExtendedHitArea(uint32 window_id,
                                              int32 x_offset,
                                              int32 y_offset,
                                              mojo.Insets hit_area);
 
   // Add and remove accelerators. When accelerators are registered the
   // WindowManager receives the event via OnAccelerator() rather than the
   // target window. The id is defined by the client and can be used to more
   // easily identify the accelerator's action. If an accelerator with the same
   // id or the same matcher already exists, then the accelerator is not added.
+  // Accelerator ID 1 << 24 and above are reserved for internal use.

[msw, 2016/05/06 22:34:31]

The int32 space is 4,294,967,295, this would reserve a disproportionately large
block of that for debug accelerators (a total of 4,293,290,080 numbers are
greater than 16,777,216). Maybe use numbers 1 << 31 and above for debug, that
reserves half the available space, which still seems unnecessarily large (for
now, time will tell...), but also supports an equally unnecessarily large space
of numbers for actual accelerators.

[James Cook, 2016/05/07 00:03:10]

Done.

   AddAccelerator(uint32 id, EventMatcher matcher) => (bool success);
   RemoveAccelerator(uint32 id);
 
   // The window manager has completed a request with the specific change id.
   WmResponse(uint32 change_id, bool response);
 
   // Calls WindowTreeClient::RequestClose() on the embedded app at the
   // specified window.
   WmRequestClose(uint32 window_id);
 
   // Sets the frame decoration constants of the display the window manager is
   // associated with.
   WmSetFrameDecorationValues(FrameDecorationValues values);
 
   // Response from WmCreateTopLevelWindow() informing the client of the id for
   // the new window.
   OnWmCreatedTopLevelWindow(uint32 change_id, uint32 window_id);
 };