[Presentation API] 1-UA presentation support + presenter APIs.

chrome/browser/extensions/api/tab_capture/offscreen_presentation.cc

Index: chrome/browser/extensions/api/tab_capture/offscreen_presentation.cc
diff --git a/chrome/browser/extensions/api/tab_capture/offscreen_presentation.cc b/chrome/browser/extensions/api/tab_capture/offscreen_presentation.cc
index 2ccd614b8035321582aac9c7c12777da22d06bdf..36dbf847d7590f24b64d6d78bc03e5e1d2ce1aad 100644
--- a/chrome/browser/extensions/api/tab_capture/offscreen_presentation.cc
+++ b/chrome/browser/extensions/api/tab_capture/offscreen_presentation.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "chrome/browser/extensions/api/tab_capture/tab_capture_registry.h"
+#include "chrome/browser/media/router/receiver_presentation_service_delegate_impl.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/web_contents_sizer.h"
 #include "content/public/browser/render_widget_host_view.h"
@@ -219,6 +220,10 @@ void OffscreenPresentation::Start(const gfx::Size& initial_size) {
   // automatically unmuted, but will be captured into the MediaStream.
   presentation_web_contents_->SetAudioMuted(true);
 
+  // Register the offscreen tab as the receiver of the offscreen presentation.
+  media_router::ReceiverPresentationServiceDelegateImpl::CreateForWebContents(
+      presentation_web_contents_.get(), presentation_id());
+
   // Navigate to the initial URL of the presentation.
   content::NavigationController::LoadURLParams load_params(start_url_);
   load_params.should_replace_current_entry = true;