PlzNavigate: add cancel navigation logic for uncommitted requests

content/browser/frame_host/navigation_request.h

Index: content/browser/frame_host/navigation_request.h
diff --git a/content/browser/frame_host/navigation_request.h b/content/browser/frame_host/navigation_request.h
index 6cc1cd2fe98b6bcaf4a44e74ae2e4f66ffeb3eca..55a8e82011a33e40bf170de02d9a4935cee20042 100644
--- a/content/browser/frame_host/navigation_request.h
+++ b/content/browser/frame_host/navigation_request.h
@@ -18,6 +18,8 @@ class ResourceRequestBody;
 // ResourceDispatcherHost (that lives on the IO thread).
 // TODO(clamy): Describe the interactions between the UI and IO thread during
 // the navigation following its refactoring.
+// TODO(carlosk): move navigation_request_id generation to the moment when
+// the navigation is started (if that's finally required)
 class NavigationRequest {
  public:
   NavigationRequest(const NavigationRequestInfo& info, int64 frame_node_id);
@@ -32,7 +34,13 @@ class NavigationRequest {
   // manipulated on the UI thread.
   void BeginNavigation(scoped_refptr<ResourceRequestBody> body);
 
+  int64 navigation_request_id() const { return navigation_request_id_; }
+
  private:
+  // The next available browser-global navigation request ID.
+  static int64 next_navigation_request_id_;
+
+  const int64 navigation_request_id_;
   const NavigationRequestInfo info_;
   const int64 frame_node_id_;