In chromium, context menu is displayed when right mouse button is released....

views/window/window_win.h

 // Copyright (c) 2006-2008 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 VIEWS_WINDOW_WINDOW_WIN_H_
 #define VIEWS_WINDOW_WINDOW_WIN_H_
 
 #include "views/widget/widget_win.h"
 #include "views/window/window.h"
 
@@ skipping 106 matching lines @@
   virtual void OnFinalMessage(HWND window);
   virtual void OnGetMinMaxInfo(MINMAXINFO* minmax_info);
   virtual void OnInitMenu(HMENU menu);
   virtual void OnMouseLeave();
   virtual LRESULT OnNCActivate(BOOL active);
   virtual LRESULT OnNCCalcSize(BOOL mode, LPARAM l_param);
   virtual LRESULT OnNCHitTest(const CPoint& point);
   virtual void OnNCPaint(HRGN rgn);
   virtual void OnNCLButtonDown(UINT ht_component, const CPoint& point);
   virtual void OnNCRButtonDown(UINT ht_component, const CPoint& point);
+  virtual void OnNCRButtonUp(UINT ht_component, const CPoint& point);
+  virtual void OnRButtonUp(UINT ht_component, const CPoint& point);
   virtual LRESULT OnNCUAHDrawCaption(UINT msg, WPARAM w_param, LPARAM l_param);
   virtual LRESULT OnNCUAHDrawFrame(UINT msg, WPARAM w_param, LPARAM l_param);
   virtual LRESULT OnSetCursor(HWND window, UINT hittest_code, UINT message);
   virtual LRESULT OnSetIcon(UINT size_type, HICON new_icon);
   virtual LRESULT OnSetText(const wchar_t* text);
   virtual void OnSettingChange(UINT flags, const wchar_t* section);
   virtual void OnSize(UINT size_param, const CSize& new_size);
   virtual void OnSysCommand(UINT notification_code, CPoint click);
   virtual void OnWindowPosChanging(WINDOWPOS* window_pos);
   virtual Window* GetWindow() { return this; }
@@ skipping 132 matching lines @@
   // The following factory is used to ignore SetWindowPos() calls for short time
   // periods.
   ScopedRunnableMethodFactory<WindowWin> ignore_pos_changes_factory_;
 
   // If this is greater than zero, we should prevent attempts to make the window
   // visible when we handle WM_WINDOWPOSCHANGING. Some calls like
   // ShowWindow(SW_RESTORE) make the window visible in addition to restoring it,
   // when all we want to do is restore it.
   int force_hidden_count_;
 
+  // Set to true when the user presses the right mouse button on the caption
+  // area. We need this so we can correctly show the context menu on mouse-up.
+  bool is_right_mouse_pressed_on_caption_;
+
   // The last-seen monitor containing us, and its rect and work area.  These are
   // used to catch updates to the rect and work area and react accordingly.
   HMONITOR last_monitor_;
   gfx::Rect last_monitor_rect_, last_work_area_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowWin);
 };
 
 }  // namespace views
 
 #endif  // VIEWS_WINDOW_WINDOW_WIN_H_