Adds ability for pre-target accelerators to not consume events

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index a15f7bf5c7117e6b21cc6037a3bb34d943b92fab..ecc0a20bd11cffcd265d42983492b529c3d47128 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -29,6 +29,19 @@ import "ui/platform_window/mojo/text_input_state.mojom";
 // rather than a callback to ensure ordering. The server does not interpret the
 // change id in anyway, it is up to the client to assign a value and use it.
 // Generally the change id is an ever increasing integer.
+//
+// Event processing happens in the following order:
+// . The event is sent to the accelerator registered for the PRE_TARGET. If
+//   the client consumes the event, matching event observers are notified and
+//   processing stops. If the EventMatcher does not consume the event processing

[sadrul, 2016/07/07 20:04:42]

Do you mean 'If the accelerator handler does not consume the event ...'?

[sky, 2016/07/07 21:55:42]

I changed it to client as that is what I said on the previous line.

+//   continues.
+// . Target window (lookup of the target window depends upon the event type) and
+//   matching event observers and notified at the same time. The target is only

[sadrul, 2016/07/07 20:04:42]

s/and/are

[sky, 2016/07/07 21:55:43]

Done.

+//   notified once, even if it has a matching event observer registered. If the
+//   target consumes the event, processing stops.

[sadrul, 2016/07/07 20:04:41]

What happens if there is a non-accelerator event for the target, but the
accelerator is yet to be acked by the window manager?

[sky, 2016/07/07 21:55:42]

Not sure what you mean. If there is no-accelerator than we aren't blocked
waiting for the wm. OTOH if there is an accelerator then step 1 waits until we
get the ack from the wm. Maybe I'm misunderstanding your question?

+// . Accelerator registered for POST_TARGET. No response is expected from the
+//   client for the POST_TARGET and processing of the next continues
+//   immediately.
 interface WindowTree {
   // Creates a new window with the specified id. It is up to the client to
   // ensure the id is unique to the connection (the id need not be globally
@@ -73,6 +86,8 @@ interface WindowTree {
   // this window tree) or OnEventObserved (if the target is another tree). The
   // client must supply a non-zero |observer_id|, which is reported back with
   // observed events.  Set the matcher to null to clear the observer.
+  //
+  // See class description for details on event delivery.
   SetEventObserver(EventMatcher? matcher, uint32 observer_id);
 
   // Sets the specified bounds of the specified window.