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

content/public/browser/presentation_service_delegate.h

Index: content/public/browser/presentation_service_delegate.h
diff --git a/content/public/browser/presentation_service_delegate.h b/content/public/browser/presentation_service_delegate.h
index 817cd282a8f246eac8ac6a2e7bda0ccba940f5f7..37d446904fb9740efb253cca7ae4f4443b0b07e4 100644
--- a/content/public/browser/presentation_service_delegate.h
+++ b/content/public/browser/presentation_service_delegate.h
@@ -31,6 +31,7 @@ class CONTENT_EXPORT PresentationServiceDelegate {
       base::Callback<void(const PresentationSessionInfo&)>;
   using PresentationSessionErrorCallback =
       base::Callback<void(const PresentationError&)>;
+  using SendMessageCallback = base::Callback<void()>;
 
   virtual ~PresentationServiceDelegate() {}
 
@@ -115,6 +116,20 @@ class CONTENT_EXPORT PresentationServiceDelegate {
       const std::string& presentation_id,
       const PresentationSessionSuccessCallback& success_cb,
       const PresentationSessionErrorCallback& error_cb) = 0;
+
+  // Sends a string message to a presentation session.
+  // |render_process_id|, |render_frame_id|: ID of originating frame.
+  // |presentation_url|: URL of the presentation.
+  // |presentation_id|: ID of the presentation.
+  // |message|: message to be sent.
+  // |send_message_cb|: Invoked when message is sent.
+  virtual void SendStringMessage(
+      int render_process_id,
+      int render_frame_id,
+      const std::string& presentation_url,
+      const std::string& presentation_id,
+      const std::string& message,
+      const SendMessageCallback& send_message_cb) = 0;
 };
 
 }  // namespace content