Create only a single LegacyRenderWidgetHostHWND per WebContentsViewAura.

content/browser/renderer_host/legacy_render_widget_host_win.h

 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_LEGACY_RENDER_WIDGET_HOST_WIN_H_
 #define CONTENT_BROWSER_RENDERER_HOST_LEGACY_RENDER_WIDGET_HOST_WIN_H_
 
 #include <atlbase.h>
 #include <atlcrack.h>
 #include <atlwin.h>
 #include <oleacc.h>
 
 #include <memory>
 
 #include "base/macros.h"
 #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 {
 class DirectManipulationHelper;
 }  // namespace win
 }  // namespace gfx
 
 namespace ui {
 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.
 //    With Aura there is one main HWND which comprises the whole browser window
 //    or the whole desktop. So, we need a fake HWND with the window class as
 //    Chrome_RenderWidgetHostHWND as the root of the accessibility tree for
 //    each tab.
 // 2. There are legacy drivers for trackpads/trackpoints which have special
 //    code for sending mouse wheel and scroll events to the
 //    Chrome_RenderWidgetHostHWND window.
 // 3. Windowless NPAPI plugins like Flash and Silverlight which expect the
 //    container window to have the same bounds as the web page. In Aura, the
 //    default container window is the whole window which includes the web page
 //    WebContents, etc. This causes the plugin mouse event calculations to
 //    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,
                            NON_EXPORTED_BASE(ATL::CWindow),
                            ATL::CWinTraits<WS_CHILD> > Base;
 
   // 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)
     MESSAGE_RANGE_HANDLER(WM_KEYFIRST, WM_KEYLAST, OnKeyboardRange)
     MESSAGE_HANDLER_EX(WM_PAINT, OnPaint)
     MESSAGE_HANDLER_EX(WM_NCPAINT, OnNCPaint)
     MESSAGE_HANDLER_EX(WM_ERASEBKGND, OnEraseBkGnd)
     MESSAGE_RANGE_HANDLER(WM_MOUSEFIRST, WM_MOUSELAST, OnMouseRange)
     MESSAGE_HANDLER_EX(WM_MOUSELEAVE, OnMouseLeave)
     MESSAGE_HANDLER_EX(WM_MOUSEACTIVATE, OnMouseActivate)
     MESSAGE_HANDLER_EX(WM_SETCURSOR, OnSetCursor)
     MESSAGE_HANDLER_EX(WM_TOUCH, OnTouch)
     MESSAGE_HANDLER_EX(WM_HSCROLL, OnScroll)
     MESSAGE_HANDLER_EX(WM_VSCROLL, OnScroll)
     MESSAGE_HANDLER_EX(WM_NCHITTEST, OnNCHitTest)
     MESSAGE_RANGE_HANDLER(WM_NCMOUSEMOVE, WM_NCXBUTTONDBLCLK,
                           OnMouseRange)
     MESSAGE_HANDLER_EX(WM_NCCALCSIZE, OnNCCalcSize)
     MESSAGE_HANDLER_EX(WM_SIZE, OnSize)
     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.
   // The |parent| parameter contains the new parent window.
   void UpdateParent(HWND parent);
   HWND GetParent();
 
   IAccessible* window_accessible() { return window_accessible_.get(); }
 
   // Functions to show and hide the window.
   void Show();
   void Hide();
 
   // 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();
 
   // Returns the target to which the windows input events are forwarded.
   static ui::WindowEventTarget* GetWindowEventTarget(HWND parent);
 
   LRESULT OnEraseBkGnd(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnGetObject(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnKeyboardRange(UINT message, WPARAM w_param, LPARAM l_param,
                           BOOL& handled);
   LRESULT OnMouseLeave(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnMouseRange(UINT message, WPARAM w_param, LPARAM l_param,
                        BOOL& handled);
   LRESULT OnMouseActivate(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnTouch(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnScroll(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnNCHitTest(UINT message, WPARAM w_param, LPARAM l_param);
 
   LRESULT OnNCPaint(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnPaint(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnSetCursor(UINT message, WPARAM w_param, LPARAM l_param);
   LRESULT OnNCCalcSize(UINT message, WPARAM w_param, LPARAM l_param);
   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.
   std::unique_ptr<gfx::win::DirectManipulationHelper>
       direct_manipulation_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(LegacyRenderWidgetHostHWND);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_LEGACY_RENDER_WIDGET_HOST_WIN_H_
-