[Presentation API] Plumbing the |defaultpresentationstart| event from Blink to browser/Mojo.

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 65e729f49bd85d0c73f5ba844c23837237dedf05..d08157f02478e5025020e4f47485152ea8e18fd4 100644
--- a/content/browser/presentation/presentation_service_impl.h
+++ b/content/browser/presentation/presentation_service_impl.h
@@ -54,6 +54,8 @@ class CONTENT_EXPORT PresentationServiceImpl
   using NewSessionMojoCallback =
       mojo::Callback<void(presentation::PresentationSessionInfoPtr,
           presentation::PresentationErrorPtr)>;
+  using DefaultPresentationMojoCallback =
+      mojo::Callback<void(presentation::PresentationSessionInfoPtr)>;
 
   friend class PresentationServiceImplTest;
   FRIEND_TEST_ALL_PREFIXES(PresentationServiceImplTest, RemoveAllListeners);
@@ -80,6 +82,8 @@ class CONTENT_EXPORT PresentationServiceImpl
       const mojo::String& presentation_url,
       const ScreenAvailabilityMojoCallback& callback) override;
   void OnScreenAvailabilityListenerRemoved() override;
+  void ListenForDefaultPresentationStart(
+      const DefaultPresentationMojoCallback& callback) override;
   void StartSession(
       const mojo::String& presentation_url,
       const mojo::String& presentation_id,