[Media Router] Add a presentation id to MediaRoute mapping in the MR

chrome/browser/media/router/media_route.h

Index: chrome/browser/media/router/media_route.h
diff --git a/chrome/browser/media/router/media_route.h b/chrome/browser/media/router/media_route.h
index e2715846d60c73ef1d42b1bf941c67c182e7c64f..d21cec38a03ce9a819c2ef9a3d3ed61e60de9113 100644
--- a/chrome/browser/media/router/media_route.h
+++ b/chrome/browser/media/router/media_route.h
@@ -91,6 +91,13 @@ class MediaRoute {
   }
   bool is_offscreen_presentation() const { return is_offscreen_presentation_; }
 
+  void set_presentation_id(const std::string& presentation_id) {
+    presentation_id_ = presentation_id;
+  }
+  const base::Optional<std::string>& presentation_id() const {
+    return presentation_id_;
+  }
+
   bool Equals(const MediaRoute& other) const;
 
  private:
@@ -125,6 +132,9 @@ class MediaRoute {
   // |true| if the presentation associated with this route is an offscreen
   // presentation.
   bool is_offscreen_presentation_ = false;
+
+  // Presentation id associated with this media route object.
+  base::Optional<std::string> presentation_id_;
 };
 
 }  // namespace media_router