Prevent reentry in FrameView::Dispose

With embedded_content_view_ set to its new value before the call to
Dispose(), that method will no longer recurse back into
SetEmbeddedContentView (and again into Dispose()).

Change-Id: I4397616d1b41159380145ef364d88a6448909900
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1802116Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697579}

third_party/blink/renderer/core/html/html_frame_owner_element.cc

@@ -356,17 +356,18 @@ void HTMLFrameOwnerElement::SetEmbeddedContentView(
     }
   }
 
-  if (embedded_content_view_) {
-    if (embedded_content_view_->IsAttached()) {
-      embedded_content_view_->DetachFromLayout();
-      if (embedded_content_view_->IsPluginView())
-        DisposePluginSoon(ToWebPluginContainerImpl(embedded_content_view_));
+  EmbeddedContentView* old_view = embedded_content_view_.Get();
+  embedded_content_view_ = embedded_content_view;
+  if (old_view) {
+    if (old_view->IsAttached()) {
+      old_view->DetachFromLayout();
+      if (old_view->IsPluginView())
+        DisposePluginSoon(ToWebPluginContainerImpl(old_view));
       else
-        embedded_content_view_->Dispose();
+        old_view->Dispose();
     }
   }
 
-  embedded_content_view_ = embedded_content_view;
   FrameOwnerPropertiesChanged();
 
   GetDocument().GetRootScrollerController().DidUpdateIFrameFrameView(*this);