Support custom message filtering on Mojo binding objects

mojo/public/cpp/bindings/binding.h

Index: mojo/public/cpp/bindings/binding.h
diff --git a/mojo/public/cpp/bindings/binding.h b/mojo/public/cpp/bindings/binding.h
index 8c9ee2f0c5292c9eaa0d5f534cc3352d0eed9aee..2ae539c51c44245056643344d8d3459494d09cb7 100644
--- a/mojo/public/cpp/bindings/binding.h
+++ b/mojo/public/cpp/bindings/binding.h
@@ -21,6 +21,7 @@
 namespace mojo {
 
 class AssociatedGroup;
+class MessageReceiver;
 
 // Represents the binding of an interface implementation to a message pipe.
 // When the |Binding| object is destroyed, the binding between the message pipe
@@ -152,6 +153,13 @@ class Binding {
     Bind(request.PassMessagePipe(), std::move(runner));
   }
 
+  // Adds a message filter to be notified of each incoming message and
+  // optionally prevent it from being dispatched. Filters cannot be removed.

[yzshen1, 2016/08/24 20:47:55]

Returning false not just prevents the message from being dispatched, but also
disconnects the pipe.

(I think that behavior is fine for now. Please consider updating the comment)

[Ken Rockot(use gerrit already), 2016/08/24 20:56:38]

Done

+  void AddFilter(std::unique_ptr<MessageReceiver> filter) {
+    DCHECK(is_bound());
+    internal_state_.AddFilter(std::move(filter));
+  }
+
   // Whether there are any associated interfaces running on the pipe currently.
   bool HasAssociatedInterfaces() const {
     return internal_state_.HasAssociatedInterfaces();