[TEST] Check when the BackForward PageTransition is dropped.

content/browser/frame_host/navigation_handle_impl.cc

Index: content/browser/frame_host/navigation_handle_impl.cc
diff --git a/content/browser/frame_host/navigation_handle_impl.cc b/content/browser/frame_host/navigation_handle_impl.cc
index 2ad3b58d6da54e04fd0c9660f62c82ad4e39416d..cb381cc5058fce9fe9272953af86c6326e357941 100644
--- a/content/browser/frame_host/navigation_handle_impl.cc
+++ b/content/browser/frame_host/navigation_handle_impl.cc
@@ -744,6 +744,11 @@ void NavigationHandleImpl::DidCommitNavigation(
   DCHECK_EQ(frame_tree_node_, render_frame_host->frame_tree_node());
   CHECK_EQ(url_, params.url);
 
+  // Will crash when the transition was FORWARD_BACK and becomes something else
+  // for mysterious reasons.
+  CHECK(!(transition_ & ui::PAGE_TRANSITION_FORWARD_BACK) ||
+        params.transition & ui::PAGE_TRANSITION_FORWARD_BACK);

[Charlie Reis, 2017/06/27 03:59:29]

Are you worried at all about the other direction?  It seems odd to allow cases
that FORWARD_BACK wasn't initially true but becomes true during the navigation. 
(That is, I'm curious why this is an A => B check instead of A == B.)

+
   did_replace_entry_ = did_replace_entry;
   method_ = params.method;
   has_user_gesture_ = (params.gesture == NavigationGestureUser);