Create only a single LegacyRenderWidgetHostHWND per WebContentsViewAura.

content/browser/renderer_host/legacy_render_widget_host_win.h

Index: content/browser/renderer_host/legacy_render_widget_host_win.h
diff --git a/content/browser/renderer_host/legacy_render_widget_host_win.h b/content/browser/renderer_host/legacy_render_widget_host_win.h
index ab2d635e55df4bf4ff7a4ed4140f8a59a28a9bf0..bc496cf62966b290d0755754ae269343ac1517b4 100644
--- a/content/browser/renderer_host/legacy_render_widget_host_win.h
+++ b/content/browser/renderer_host/legacy_render_widget_host_win.h
@@ -16,6 +16,7 @@
 #include "base/win/scoped_comptr.h"
 #include "content/common/content_export.h"
 #include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/native_widget_types.h"
 
 namespace gfx {
 namespace win {
@@ -28,8 +29,6 @@ class WindowEventTarget;
 }
 
 namespace content {
-class RenderWidgetHostViewAura;
-
 // Reasons for the existence of this class outlined below:-
 // 1. Some screen readers expect every tab / every unique web content container
 //    to be in its own HWND with class name Chrome_RenderWidgetHostHWND.
@@ -47,17 +46,18 @@ class RenderWidgetHostViewAura;
 //    fail.
 //    We should look to get rid of this code when all of the above are fixed.
 
+class LegacyRenderWidgetHostHWNDDelegate;
+
 // This class implements a child HWND with the same size as the content area,
-// that delegates its accessibility implementation to the root of the
-// BrowserAccessibilityManager tree. This HWND is hooked up as the parent of
-// the root object in the BrowserAccessibilityManager tree, so when any
-// accessibility client calls ::WindowFromAccessibleObject, they get this
-// HWND instead of the DesktopWindowTreeHostWin.
+// and delegates its accessibility implementation to the
+// gfx::NativeViewAccessible provided by the owner class.
 class CONTENT_EXPORT LegacyRenderWidgetHostHWND
     : public ATL::CWindowImpl<LegacyRenderWidgetHostHWND,
                               NON_EXPORTED_BASE(ATL::CWindow),
                               ATL::CWinTraits<WS_CHILD> > {
  public:
+  ~LegacyRenderWidgetHostHWND() override;
+
   DECLARE_WND_CLASS_EX(L"Chrome_RenderWidgetHostHWND", CS_DBLCLKS, 0);
 
   typedef ATL::CWindowImpl<LegacyRenderWidgetHostHWND,
@@ -67,10 +67,9 @@ class CONTENT_EXPORT LegacyRenderWidgetHostHWND
   // Creates and returns an instance of the LegacyRenderWidgetHostHWND class on
   // successful creation of a child window parented to the parent window passed
   // in.
-  static LegacyRenderWidgetHostHWND* Create(HWND parent);
-
-  // Destroys the HWND managed by this class.
-  void Destroy();
+  static LegacyRenderWidgetHostHWND* Create(
+      HWND parent,
+      LegacyRenderWidgetHostHWNDDelegate* delegate);
 
   BEGIN_MSG_MAP_EX(LegacyRenderWidgetHostHWND)
     MESSAGE_HANDLER_EX(WM_GETOBJECT, OnGetObject)
@@ -93,6 +92,8 @@ class CONTENT_EXPORT LegacyRenderWidgetHostHWND
     MESSAGE_HANDLER_EX(WM_WINDOWPOSCHANGED, OnWindowPosChanged)
   END_MSG_MAP()
 
+  // May be deleted at any time by Windows! Other classes should never store
+  // this value.
   HWND hwnd() { return m_hWnd; }
 
   // Called when the child window is to be reparented to a new window.
@@ -109,18 +110,9 @@ class CONTENT_EXPORT LegacyRenderWidgetHostHWND
   // Resizes the window to the bounds passed in.
   void SetBounds(const gfx::Rect& bounds);
 
-  // The pointer to the containing RenderWidgetHostViewAura instance is passed
-  // here.
-  void set_host(RenderWidgetHostViewAura* host) {
-    host_ = host;
-  }
-
- protected:
-  void OnFinalMessage(HWND hwnd) override;
-
  private:
-  explicit LegacyRenderWidgetHostHWND(HWND parent);
-  ~LegacyRenderWidgetHostHWND() override;
+  LegacyRenderWidgetHostHWND(HWND parent,
+                             LegacyRenderWidgetHostHWNDDelegate* delegate);
 
   bool Init();
 
@@ -146,13 +138,13 @@ class CONTENT_EXPORT LegacyRenderWidgetHostHWND
   LRESULT OnSize(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnWindowPosChanged(UINT message, WPARAM w_param, LPARAM l_param);
 
+  LegacyRenderWidgetHostHWNDDelegate* delegate_;
+
   base::win::ScopedComPtr<IAccessible> window_accessible_;
 
   // Set to true if we turned on mouse tracking.
   bool mouse_tracking_enabled_;
 
-  RenderWidgetHostViewAura* host_;
-
   // This class provides functionality to register the legacy window as a
   // Direct Manipulation consumer. This allows us to support smooth scroll
   // in Chrome on Windows 10.
@@ -165,4 +157,3 @@ class CONTENT_EXPORT LegacyRenderWidgetHostHWND
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_LEGACY_RENDER_WIDGET_HOST_WIN_H_
-