Implements ListenForSessionMessages in PresentationServiceImpl; uses Swap to avoid copying large da…

content/browser/presentation/presentation_service_impl.h

Index: content/browser/presentation/presentation_service_impl.h
diff --git a/content/browser/presentation/presentation_service_impl.h b/content/browser/presentation/presentation_service_impl.h
index fd85fe8f3444207f03aca3fe1093b846633894df..299fe7de527e6980eb9357ed6c6888ae8f9a9115 100644
--- a/content/browser/presentation/presentation_service_impl.h
+++ b/content/browser/presentation/presentation_service_impl.h
@@ -28,6 +28,7 @@ namespace content {
 
 struct FrameNavigateParams;
 struct LoadCommittedDetails;
+struct PresentationSessionMessage;
 class RenderFrameHost;
 
 // Implementation of Mojo PresentationService.
@@ -267,6 +268,12 @@ class CONTENT_EXPORT PresentationServiceImpl
       const std::string& presentation_id,
       const NewSessionMojoCallback& callback);
 
+  void OnSessionMessages(

[whywhat, 2015/05/01 15:26:12]

Please, document that for optimization purposes, this method will empty the
messages passed to it.
On the related note, do we know if copying the messages would be so bad? How
often to pages send messages and how big the payload typically is?

[haibinlu, 2015/05/01 19:03:20]

Done. Message size is up to 64KB. With get-next-batch-message pattern, messages
will be sent as fast as blink+MR can handle. With copying, each message will be
copied at least 4 times along the way, one per each end of the two mojo pipes
when converting to/from mojo message struct type.

+      scoped_ptr<ScopedVector<PresentationSessionMessage>> messages);
+
+  static presentation::SessionMessagePtr ToMojoSessionMessage(

[whywhat, 2015/05/01 15:26:12]

move to the .cc file and the unnamed namespace? doesn't have to be a class
member.

[haibinlu, 2015/05/01 19:03:20]

Done.

+      content::PresentationSessionMessage* input);
+
   // Removes the head of the queue (which represents the request that has just
   // been processed).
   // Checks if there are any queued StartSession requests and if so, executes
@@ -318,6 +325,8 @@ class CONTENT_EXPORT PresentationServiceImpl
   // The binding is removed when binding_ is cleared or goes out of scope.
   scoped_ptr<mojo::Binding<presentation::PresentationService>> binding_;
 
+  scoped_ptr<SessionMessagesCallback> on_session_messages_;

[whywhat, 2015/05/01 15:26:12]

nit: postfix the name with callback_. without knowing the type this looks like a
vector of messages, not a callback.

[haibinlu, 2015/05/01 19:03:20]

Done.

+
   // ID of the RenderFrameHost this object is associated with.
   int render_process_id_;
   int render_frame_id_;