Implement throttling behavior for LocalStorage mojo messages.

mojo/public/cpp/bindings/interface_endpoint_client.h

 // 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_ENDPOINT_CLIENT_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_ENDPOINT_CLIENT_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 59 matching lines @@
     DCHECK(thread_checker_.CalledOnValidThread());
     return encountered_error_;
   }
 
   // Returns true if this endpoint has any pending callbacks.
   bool has_pending_responders() const {
     DCHECK(thread_checker_.CalledOnValidThread());
     return !async_responders_.empty() || !sync_responses_.empty();
   }
 
+  size_t pending_responder_count() const {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    return async_responders_.size();
+  }
+
   AssociatedGroupController* group_controller() const {
     return handle_.group_controller();
   }
   AssociatedGroup* associated_group();
   uint32_t interface_id() const;
 
   // Adds a MessageReceiver which can filter a message after validation but
   // before dispatch.
   void AddFilter(std::unique_ptr<MessageReceiver> filter);
 
@@ skipping 91 matching lines @@
   base::ThreadChecker thread_checker_;
 
   base::WeakPtrFactory<InterfaceEndpointClient> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(InterfaceEndpointClient);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_INTERFACE_ENDPOINT_CLIENT_H_