[PresentationAPI] Implementing send() from WebPresentationClient to the PresentationService.

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..b948e2054de20485b4977a01c9c7e15de9c5693b 100644
--- a/content/browser/presentation/presentation_service_impl.h
+++ b/content/browser/presentation/presentation_service_impl.h
@@ -163,6 +163,10 @@ class CONTENT_EXPORT PresentationServiceImpl
       const mojo::String& presentation_url,
       const mojo::String& presentation_id,
       const NewSessionMojoCallback& callback) override;
+  void PostMessage(
+      const mojo::String& presentation_url,
+      const mojo::String& presentation_id,
+      const mojo::String& message) override;
   void CloseSession(
       const mojo::String& presentation_url,
       const mojo::String& presentation_id) override;