[PresentationAPI] Ensures only one pending message callback at a time if a frame created multiple s…

content/renderer/presentation/presentation_dispatcher.cc

Index: content/renderer/presentation/presentation_dispatcher.cc
diff --git a/content/renderer/presentation/presentation_dispatcher.cc b/content/renderer/presentation/presentation_dispatcher.cc
index 6691be68207d752afcfe8c499db8a2098a000cab..08ec8cf23359a2f20059d93275a3cf59d1427b54 100644
--- a/content/renderer/presentation/presentation_dispatcher.cc
+++ b/content/renderer/presentation/presentation_dispatcher.cc
@@ -83,7 +83,8 @@ PresentationDispatcher::PresentationDispatcher(RenderFrame* render_frame)
       controller_(nullptr),
       binding_(this),
       listening_state_(ListeningState::Inactive),
-      last_known_availability_(false) {
+      last_known_availability_(false),
+      listening_for_messages_(false) {
 }
 
 PresentationDispatcher::~PresentationDispatcher() {
@@ -337,6 +338,8 @@ void PresentationDispatcher::DidCommitProvisionalLoad(
   // Remove all pending send message requests.
   MessageRequestQueue empty;
   std::swap(message_request_queue_, empty);
+
+  listening_for_messages_ = false;
 }
 
 void PresentationDispatcher::OnScreenAvailabilityUpdated(bool available) {
@@ -388,9 +391,12 @@ void PresentationDispatcher::OnSessionCreated(
 
   DCHECK(!session_info.is_null());
   callback->onSuccess(new PresentationSessionClient(session_info.Pass()));
-  presentation_service_->ListenForSessionMessages(
-      base::Bind(&PresentationDispatcher::OnSessionMessagesReceived,
-                 base::Unretained(this)));
+  if (!listening_for_messages_) {
+    listening_for_messages_ = true;
+    presentation_service_->ListenForSessionMessages(
+       base::Bind(&PresentationDispatcher::OnSessionMessagesReceived,
+                   base::Unretained(this)));
+  }
 }
 
 void PresentationDispatcher::OnSessionStateChange(
@@ -411,9 +417,13 @@ void PresentationDispatcher::OnSessionStateChange(
 
 void PresentationDispatcher::OnSessionMessagesReceived(
     mojo::Array<presentation::SessionMessagePtr> messages) {
+  DCHECK(listening_for_messages_);

[imcheng (use chromium acct), 2015/07/07 22:24:38]

Is it possible for DidCommitProvisionalLoad() to be called right before this,
which will fail the DCHECK?

[haibinlu, 2015/07/07 22:37:24]

good point. updated.

+
   // When messages is null, there is an error at presentation service side.
-  if (!controller_ || messages.is_null())
+  if (!controller_ || messages.is_null()) {

[imcheng (use chromium acct), 2015/07/07 22:24:39]

So, we don't use an empty list for |messages| to denote error?

[haibinlu, 2015/07/07 22:37:24]

right. no empty list. presentation_service_impl converts it to an null list.

+    listening_for_messages_ = false;
     return;
+  }
 
   for (size_t i = 0; i < messages.size(); ++i) {
     if (messages[i]->type ==