Allow asynchronous deferral in NavigationSimulator

content/browser/frame_host/navigation_handle_impl.h

Index: content/browser/frame_host/navigation_handle_impl.h
diff --git a/content/browser/frame_host/navigation_handle_impl.h b/content/browser/frame_host/navigation_handle_impl.h
index e9cb20983e0c94bfd343b693d330b7b89ecdf3ad..1311dbdf742549fc58109001060d2e44aa24b2c0 100644
--- a/content/browser/frame_host/navigation_handle_impl.h
+++ b/content/browser/frame_host/navigation_handle_impl.h
@@ -346,6 +346,11 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
     response_headers_ = response_headers;
   }
 
+  void set_complete_callback_for_testing(
+      const ThrottleChecksFinishedCallback& callback) {
+    complete_callback_for_testing_ = callback;
+  }
+
  private:
   friend class NavigationHandleImplTest;
 
@@ -447,9 +452,13 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
   // The mixed content context type for potential mixed content checks.
   blink::WebMixedContentContextType mixed_content_context_type_;
 
-  // This callback will be run when all throttle checks have been performed.
+  // This callback will be run when all throttle checks have been performed. Be
+  // careful about relying on it as it may be going away.

[engedy, 2017/03/07 15:24:56]

nit: I am not sure I understand this comment.

[Charlie Harrison, 2017/03/07 16:42:43]

This was indicated by clamy in the subframe navigation filtering throttle CL:
"I really don't want to be modifying the semantic of the callback right now. We
will do it in the future though, where either NavigationHandle will be merged in
the NavigationRequest or NavigationRequest methods will be called directly by
NavigationHandle. This will result in the callback disappearing."

This is why we are adding a new for_testing_ callback instead of reusing this
one.

[engedy, 2017/03/09 11:41:34]

Got it. Let's try to clarify in the comment that "going away" means that the
member will be removed as part of a refactoring, not that the value of it might
become NULL eventually during runtime.

[Charlie Harrison, 2017/03/09 14:36:01]

Done.

   ThrottleChecksFinishedCallback complete_callback_;
 
+  // This callback will be run when all throttle checks have been performed.
+  ThrottleChecksFinishedCallback complete_callback_for_testing_;
+
   // PlzNavigate
   // Manages the lifetime of a pre-created ServiceWorkerProviderHost until a
   // corresponding ServiceWorkerNetworkProvider is created in the renderer.