Plumbing from WebPresentationClient to the Presentation Mojo service for

content/renderer/presentation/presentation_dispatcher.cc

+// 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.
+
+#include "content/renderer/presentation/presentation_dispatcher.h"
+
+#include "content/common/presentation/presentation_service.mojom.h"
+#include "content/public/common/service_registry.h"
+#include "content/public/renderer/render_frame.h"
+#include "third_party/WebKit/public/platform/WebPresentationController.h"
+
+namespace content {
+
+PresentationDispatcher::PresentationDispatcher(RenderFrame* render_frame)
+    : RenderFrameObserver(render_frame) {}
+
+PresentationDispatcher::~PresentationDispatcher() {}
+
+void PresentationDispatcher::setController(
+    blink::WebPresentationController* controller) {
+  // Provide the service with the callback to get the next |availablechange|
+  // event if needed.
+  if (controller != nullptr && controller_ != controller)
+    updateAvailableChangeWatched(controller->isAvailableChangeWatched());
+  controller_ = controller;
+}
+
+void PresentationDispatcher::updateAvailableChangeWatched(bool watched) {
+  ConnectToPresentationServiceIfNeeded();
+  if (watched) {
+    presentation_service_->GetScreenAvailability(
+        base::Bind(&PresentationDispatcher::OnScreenAvailabilityChanged,
+                 base::Unretained(this)));
+  }
+}
+
+void PresentationDispatcher::OnScreenAvailabilityChanged(bool available) {
+  if (!controller_)
+    return;
+
+  controller_->didChangeAvailability(available);
+
+  // Reset the callback to get the next event.
+  updateAvailableChangeWatched(controller_->isAvailableChangeWatched());

[blundell, 2015/01/26 10:31:08]

You should call this before line 41 as you don't know what side-effects line 41
will have (will it e.g. possibly delete |this| in some future world?).

[whywhat, 2015/01/26 11:06:08]

Done.

+}
+
+void PresentationDispatcher::ConnectToPresentationServiceIfNeeded() {
+  if (presentation_service_.get())
+    return;
+
+  render_frame()->GetServiceRegistry()->ConnectToRemoteService(
+      &presentation_service_);
+}
+
+}  // namespace content