[Presentation API] fire onconnectionavailable and onconnect event asynchronously

We would like to ensure following execution order when calling PresentationRequest.start():

1. resolve start() promise
2. fire PresentationRequest onconnectionavailable event
3. fire PresentationConnection onconnect event

To fire event after resolving promise, we need to dispatch events asynchronously

BUG=669213

Review-Url: https://codereview.chromium.org/2547143002
Cr-Commit-Position: refs/heads/master@{#437598}

third_party/WebKit/Source/modules/presentation/PresentationConnection.cpp

@@ -9,6 +9,7 @@
 #include "core/dom/DOMArrayBufferView.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
+#include "core/dom/ExecutionContextTask.h"
 #include "core/events/Event.h"
 #include "core/events/MessageEvent.h"
 #include "core/fileapi/FileReaderLoader.h"
@@ -191,8 +192,14 @@ PresentationConnection* PresentationConnection::take(
   PresentationConnection* connection = new PresentationConnection(
       controller->frame(), client->getId(), client->getUrl());
   controller->registerConnection(connection);
-  request->dispatchEvent(PresentationConnectionAvailableEvent::create(
-      EventTypeNames::connectionavailable, connection));
+
+  // Fire onconnectionavailable event asynchronously.
+  auto* event = PresentationConnectionAvailableEvent::create(
+      EventTypeNames::connectionavailable, connection);
+  request->getExecutionContext()->postTask(
+      BLINK_FROM_HERE,
+      createSameThreadTask(&PresentationConnection::dispatchEventAsync,
+                           wrapPersistent(request), wrapPersistent(event)));
 
   return connection;
 }
@@ -415,10 +422,10 @@ void PresentationConnection::didChangeState(
       NOTREACHED();
       return;
     case WebPresentationConnectionState::Connected:
-      dispatchEvent(Event::create(EventTypeNames::connect));
+      dispatchStateChangeEvent(Event::create(EventTypeNames::connect));
       return;
     case WebPresentationConnectionState::Terminated:
-      dispatchEvent(Event::create(EventTypeNames::terminate));
+      dispatchStateChangeEvent(Event::create(EventTypeNames::terminate));
       return;
     // Closed state is handled in |didClose()|.
     case WebPresentationConnectionState::Closed:
@@ -435,7 +442,7 @@ void PresentationConnection::didClose(
     return;
 
   m_state = WebPresentationConnectionState::Closed;
-  dispatchEvent(PresentationConnectionCloseEvent::create(
+  dispatchStateChangeEvent(PresentationConnectionCloseEvent::create(
       EventTypeNames::close, connectionCloseReasonToString(reason), message));
 }
 
@@ -464,6 +471,21 @@ void PresentationConnection::didFailLoadingBlob(
   handleMessageQueue();
 }
 
+void PresentationConnection::dispatchStateChangeEvent(Event* event) {
+  getExecutionContext()->postTask(
+      BLINK_FROM_HERE,
+      createSameThreadTask(&PresentationConnection::dispatchEventAsync,
+                           wrapPersistent(this), wrapPersistent(event)));
+}
+
+// static
+void PresentationConnection::dispatchEventAsync(EventTarget* target,
+                                                Event* event) {
+  DCHECK(target);
+  DCHECK(event);
+  target->dispatchEvent(event);
+}
+
 void PresentationConnection::tearDown() {
   // Cancel current Blob loading if any.
   if (m_blobLoader) {

third_party/WebKit/Source/modules/presentation/PresentationConnection.h

@@ -114,6 +114,10 @@ class PresentationConnection final : public EventTargetWithInlineData,
   void didFinishLoadingBlob(DOMArrayBuffer*);
   void didFailLoadingBlob(FileError::ErrorCode);
 
+  // Internal helper function to dispatch state change events asynchronously.
+  void dispatchStateChangeEvent(Event*);
+  static void dispatchEventAsync(EventTarget*, Event*);
+
   // Cancel loads and pending messages when the connection is closed.
   void tearDown();