Propagate viewport intersection across OOPIFs at the correct time

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 0a34de2ebdd1c72b5513d2132c2bb5ad3adfcc90..ec116a3566c54eb0fa0e0a64c6ef9a6051b1fd1b 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4937,8 +4937,12 @@ void FrameView::UpdateViewportIntersectionsForSubtree(
 
   for (Frame* child = frame_->Tree().FirstChild(); child;
        child = child->Tree().NextSibling()) {
-    if (!child->IsLocalFrame())
+    DCHECK(child->IsRemoteFrame() || child->IsLocalFrame());

[dcheng, 2017/05/05 18:25:14]

Isn't this DCHECK always going to be true?

[kenrb, 2017/05/05 19:01:31]

Aren't *all* DCHECKs supposed to be always true? :)

I see your point, though. Violating that would be a significant change to the
Frame code and would break Blink in a lot of ways. I'll take it out.

+    if (child->IsRemoteFrame()) {
+      if (RemoteFrameView* view = ToRemoteFrame(child)->View())
+        view->UpdateRemoteViewportIntersection();

[dcheng, 2017/05/05 18:25:14]

It almost feels like View() and <update intersections> should be virtuals.
*shrug*

[kenrb, 2017/05/05 19:01:31]

That might be reasonable for View(). For UpdateViewportIntersections I think the
difference in function arguments makes it more trouble than it's worth.

[dcheng, 2017/05/05 22:47:53]

Do you mind poking at this in a followup?

FWIW, I don't think combining the methods for RemoteFrameView/FrameView is that
bad: it's just one parameter to ignore, and it removes explicit downcasts from
the codebase. I think the explicit downcasts have been a pretty big headache
overall, and using virtual dispatch will result in overall simpler to reason
about code.

       continue;
+    }
     if (FrameView* view = ToLocalFrame(child)->View())
       view->UpdateViewportIntersectionsForSubtree(target_state);
   }