Ensure LegacyRenderWidgetHostHWND is always created.

content/browser/web_contents/web_contents_view_aura.h

Index: content/browser/web_contents/web_contents_view_aura.h
diff --git a/content/browser/web_contents/web_contents_view_aura.h b/content/browser/web_contents/web_contents_view_aura.h
index 05fe1b092d1d805297f9147b2b58e7a0d6d08a56..856ccadd30c2d31f9ef04a6ea2ced1fcdf9adb49 100644
--- a/content/browser/web_contents/web_contents_view_aura.h
+++ b/content/browser/web_contents/web_contents_view_aura.h
@@ -53,6 +53,12 @@ class CONTENT_EXPORT WebContentsViewAura
   // Allow the WebContentsViewDelegate to be set explicitly.
   void SetDelegateForTesting(WebContentsViewDelegate* delegate);
 
+  // Set a flag to pass nullptr as the parent_view argument to
+  // RenderWidgetHostViewAura::InitAsChild().
+  void set_init_rwhv_with_null_parent_for_testing(bool set) {
+    init_rwhv_with_null_parent_for_testing_ = set;
+  }
+
  private:
   class WindowObserver;
 
@@ -78,6 +84,9 @@ class CONTENT_EXPORT WebContentsViewAura
   ui::TouchSelectionController* GetSelectionController() const;
   TouchSelectionControllerClientAura* GetSelectionControllerClient() const;
 
+  // Returns GetNativeView unless overridden for testing.
+  gfx::NativeView GetRenderWidgetHostViewParent() const;
+
   // Overridden from WebContentsView:
   gfx::NativeView GetNativeView() const override;
   gfx::NativeView GetContentNativeView() const override;
@@ -190,6 +199,8 @@ class CONTENT_EXPORT WebContentsViewAura
 
   std::unique_ptr<GestureNavSimple> gesture_nav_simple_;
 
+  bool init_rwhv_with_null_parent_for_testing_;
+
   DISALLOW_COPY_AND_ASSIGN(WebContentsViewAura);
 };