Clear last MouseMove root view in RWHIER if that view gets destroyed

content/browser/renderer_host/render_widget_host_input_event_router.cc

Index: content/browser/renderer_host/render_widget_host_input_event_router.cc
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.cc b/content/browser/renderer_host/render_widget_host_input_event_router.cc
index b0b580f1a0c9a1434153c6bf847f60f7f8ceefe0..6c95a3a2e6f3bcfacb673e118140584e941011f2 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.cc
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.cc
@@ -90,7 +90,7 @@ void RenderWidgetHostInputEventRouter::OnRenderWidgetHostViewBaseDestroyed(
     else
       last_mouse_move_target_ = nullptr;
 
-    if (!last_mouse_move_target_)
+    if (!last_mouse_move_target_ || view == last_mouse_move_root_view_)
       last_mouse_move_root_view_ = nullptr;
   }
 }
@@ -383,13 +383,18 @@ void RenderWidgetHostInputEventRouter::SendMouseEnterOrLeaveEvents(
   RenderWidgetHostViewBase* cur_view = target;
   entered_views.push_back(cur_view);
   while (cur_view != root_view) {
-    // Non-root RWHVs are guaranteed to be RenderWidgetHostViewChildFrames.
+    // Non-root RWHVs are guaranteed to be RenderWidgetHostViewChildFrames,
+    // as long as they are the only embeddable RWHVs.
+    CHECK(cur_view->IsRenderWidgetHostViewChildFrame());

[ncarter (slow), 2016/10/07 17:52:27]

If we can't guarantee this via static typing, then I think this approach makes
sense. A CHECK is way way better than a bad cast.

Statically typing this, would probably mean new functions to handle the root vs.
embedded frames, and updating the containers so that they explicitly held
RWHVChildFrames? In my experience the code usually winds up clearer after such
transformation.

[kenrb, 2016/10/07 18:44:24]

I'm not clear on how that would work. RWHVCF::GetParentView() can return any
kind of RenderWidgetHostView, so a static_cast is going to be necessary at some
point. Also, static typing makes it harder to adapt this later to deal with
RWHVMus.

I've uploaded what I think is a better approach to this guard that removes the
CHECK. Now there is a DCHECK and it is still resistant to bad cast bugs. If
you'd still prefer me to change this to static typing then we can chat about how
that could be done.

     cur_view =
         static_cast<RenderWidgetHostViewChildFrame*>(cur_view)->GetParentView();
     // cur_view can possibly be nullptr for guestviews that are not currently
     // connected to the webcontents tree.
-    if (!cur_view)
-      break;
+    if (!cur_view) {
+      last_mouse_move_target_ = target;
+      last_mouse_move_root_view_ = root_view;
+      return;
+    }
     entered_views.push_back(cur_view);
   }
 
@@ -397,10 +402,14 @@ void RenderWidgetHostInputEventRouter::SendMouseEnterOrLeaveEvents(
   if (cur_view) {
     exited_views.push_back(cur_view);
     while (cur_view != root_view) {
+      CHECK(cur_view->IsRenderWidgetHostViewChildFrame());
       cur_view = static_cast<RenderWidgetHostViewChildFrame*>(cur_view)
                      ->GetParentView();
-      if (!cur_view)
-        break;
+      if (!cur_view) {
+        last_mouse_move_target_ = target;
+        last_mouse_move_root_view_ = root_view;
+        return;
+      }
       exited_views.push_back(cur_view);
     }
   }