[Presentation API] Plumbing of |onstatechange| from the Mojo service to the public/platform

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 104b3ae9b92b5d79fb731a844629e0e9f1f0d941..247ec8f9f34bd595fe07cf885ce0980726fd9bd1 100644
--- a/content/browser/presentation/presentation_service_impl.h
+++ b/content/browser/presentation/presentation_service_impl.h
@@ -61,6 +61,9 @@ class CONTENT_EXPORT PresentationServiceImpl
           presentation::PresentationErrorPtr)>;
   using DefaultSessionMojoCallback =
       mojo::Callback<void(presentation::PresentationSessionInfoPtr)>;
+  using SessionStateCallback =
+      mojo::Callback<void(presentation::PresentationSessionInfoPtr,
+          presentation::PresentationSessionState)>;
 
   // A helper data class used by PresentationServiceImpl to do bookkeeping
   // of currently registered screen availability listeners.
@@ -166,6 +169,8 @@ class CONTENT_EXPORT PresentationServiceImpl
   void CloseSession(
       const mojo::String& presentation_url,
       const mojo::String& presentation_id) override;
+  void ListenForSessionStateChange(
+      const SessionStateCallback& callback) override;
 
   // mojo::InterfaceImpl override.
   // Note that this is called when the RenderFrameHost is deleted.