mus: Allow embedder to intercept events.

components/mus/public/interfaces/window_tree.mojom

Index: components/mus/public/interfaces/window_tree.mojom
diff --git a/components/mus/public/interfaces/window_tree.mojom b/components/mus/public/interfaces/window_tree.mojom
index 8aaa8b30785d759524a13f52485d20f8a4709e17..85e84f56f24e7f21dbc63b30fbe27e0166418293 100644
--- a/components/mus/public/interfaces/window_tree.mojom
+++ b/components/mus/public/interfaces/window_tree.mojom
@@ -52,6 +52,8 @@ enum EventResult {
   UNHANDLED,
 };
 
+const uint32 kEmbedFlagEmbedderInterceptsEvents = 0x01;

[Ben Goodger (Google), 2016/06/16 16:53:49]

1. Can you use an enum for this, and refer to it from Embed() below?
2. You need to document the precise behavior of this flag. Does the child
receive the event too? If not, is the embedder required to forward it? etc etc.

[sadrul, 2016/06/16 16:56:59]

I had an enum before, but switched to using ints since it looks like that's how
flags are done in mojo (e.g. ui::EventFlag equivalents in mojom as kEventFlag*)

+
 // Windows are identified by a uint32. The upper 16 bits are the connection id,
 // and the lower 16 the id assigned by the client.
 //
@@ -228,7 +230,8 @@ interface WindowTree {
   // OnEmbeddedAppDisconnected().
   //
   // The callback returns whether the embedding was successful.
-  Embed(uint32 window_id, WindowTreeClient client) => (bool success);
+  Embed(uint32 window_id, WindowTreeClient client, uint32 flags)
+      => (bool success);
 
   // Sets focus to the specified window, use 0 to clear focus. For a window to
   // get focus the following has to happen: the window is drawn, the window has