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..f097c841cc9808ebdc7642637c471a84aeae2ec8 100644
--- a/components/mus/public/interfaces/window_tree.mojom
+++ b/components/mus/public/interfaces/window_tree.mojom
@@ -52,6 +52,13 @@ enum EventResult {
   UNHANDLED,
 };
 
+// When this flag is set in a call to Embed(), the embedder (i.e. the client
+// that is making the call to Embed()) will receive events that are targeted to
+// the embedded client. The embedded client will not receive any input events
+// from the window server. However, the embedder can choose to dispatch events
+// to the embedded client through other mechanism.

[Ben Goodger (Google), 2016/06/16 17:34:36]

What other mechanism?

[sadrul, 2016/06/16 17:45:16]

In the case of chrome, the browser has another IPC channel to the renderer, and
it would use that channel for sending the events to the renderer. i.e. mus does
not provide a mechanism for the embedder to directly dispatch events to the
embedded client. The embedder/embeddee need to have a separate mechanism that
they decide on.

+const uint32 kEmbedFlagEmbedderInterceptsEvents = 0x01;
+
 // Windows are identified by a uint32. The upper 16 bits are the connection id,
 // and the lower 16 the id assigned by the client.
 //
@@ -213,6 +220,9 @@ interface WindowTree {
   // The caller must have created |window_id|. If not the request fails and the
   // response is false.
   //
+  // The embedder can dictate the behaviour of the embedded client by setting
+  // the appropriate embed flags (e.g. kEmbedFlagEmbedderInterceptsEvents).
+  //
   // When a connection embeds a WindowTreeClient the originating connection no
   // longer has privileges to access or see any of the children of the window.
   // If the window had existing children the children are removed. The
@@ -228,7 +238,8 @@ 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 embed_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