Return the outermost embedder when returning the embedder web contents.

chrome/browser/ui/views/chrome_constrained_window_views_client.cc

Index: chrome/browser/ui/views/chrome_constrained_window_views_client.cc
diff --git a/chrome/browser/ui/views/chrome_constrained_window_views_client.cc b/chrome/browser/ui/views/chrome_constrained_window_views_client.cc
index 7575b14741b9aa69c9025eb7f396e73d1d95e0cf..767d96d99b28e14fae307295dde2da2301eed301 100644
--- a/chrome/browser/ui/views/chrome_constrained_window_views_client.cc
+++ b/chrome/browser/ui/views/chrome_constrained_window_views_client.cc
@@ -21,10 +21,17 @@ class ChromeConstrainedWindowViewsClient
   // ConstrainedWindowViewsClient:
   content::WebContents* GetEmbedderWebContents(
       content::WebContents* initiator_web_contents) override {
-    extensions::GuestViewBase* guest_view =
-        extensions::GuestViewBase::FromWebContents(initiator_web_contents);
-    return guest_view && guest_view->embedder_web_contents() ?
-        guest_view->embedder_web_contents() : initiator_web_contents;
+    // |initiator_web_contents| may be embedded within a chain of nested
+    // GuestViews. If it is, follow the chain of embedders to the outermost
+    // WebContents and return it.
+    while (extensions::GuestViewBase* guest_view =
+               extensions::GuestViewBase::FromWebContents(
+                   initiator_web_contents)) {
+      if (!guest_view->embedder_web_contents())
+        break;
+      initiator_web_contents = guest_view->embedder_web_contents();
+    }
+    return initiator_web_contents;
   }
   web_modal::ModalDialogHost* GetModalDialogHost(
       gfx::NativeWindow parent) override {