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

views/window/window_win.cc

 // 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.
 
 #include "views/window/window_win.h"
 
 #include <shellapi.h>
 
 #include "app/gfx/canvas.h"
 #include "app/gfx/font.h"
@@ skipping 495 matching lines @@
       fullscreen_(false),
       window_closed_(false),
       disable_inactive_rendering_(false),
       is_active_(false),
       lock_updates_(false),
       saved_window_style_(0),
       saved_maximized_state_(0),
       ignore_window_pos_changes_(false),
       ignore_pos_changes_factory_(this),
       force_hidden_count_(0),
+      is_right_mouse_pressed_on_caption_(false),
       last_monitor_(NULL) {
   is_window_ = true;
   InitClass();
   DCHECK(window_delegate_);
   window_delegate_->window_.reset(this);
   // Initialize these values to 0 so that subclasses can override the default
   // behavior before calling Init.
   set_window_style(0);
   set_window_ex_style(0);
 }
@@ skipping 413 matching lines @@
     // scoped update lock.
     ScopedRedrawLock lock(this);
     DefWindowProc(GetNativeView(), WM_NCLBUTTONDOWN, ht_component,
                   MAKELPARAM(point.x, point.y));
     SetMsgHandled(TRUE);
   }
   */
 }
 
 void WindowWin::OnNCRButtonDown(UINT ht_component, const CPoint& point) {
-  if (ht_component == HTCAPTION || ht_component == HTSYSMENU)
-    RunSystemMenu(gfx::Point(point));
-  else
-    WidgetWin::OnNCRButtonDown(ht_component, point);
+  if (ht_component == HTCAPTION || ht_component == HTSYSMENU) {
+    is_right_mouse_pressed_on_caption_ = true;
+    // Using SetCapture() here matches Windows native behavior for right-clicks
+    // on the title bar. It's not obvious why Windows does this.
+    SetCapture();
+  }
+
+  WidgetWin::OnNCRButtonDown(ht_component, point);
+}
+
+void WindowWin::OnNCRButtonUp(UINT ht_component, const CPoint& point) {
+  if (is_right_mouse_pressed_on_caption_)
+    is_right_mouse_pressed_on_caption_ = false;
+
+  WidgetWin::OnNCRButtonUp(ht_component, point);
+}
+
+void WindowWin::OnRButtonUp(UINT ht_component, const CPoint& point) {
+  // We handle running the system menu on mouseup here because calling
+  // SetCapture() on mousedown makes the mouseup generate WM_RBUTTONUP instead
+  // of WM_NCRBUTTONUP.
+  CPoint pt = point;
+  MapWindowPoints(GetNativeView(), HWND_DESKTOP, &pt, 1);
+  if (is_right_mouse_pressed_on_caption_) {
+    is_right_mouse_pressed_on_caption_ = false;
+    ReleaseCapture();
+    ht_component =
+        ::SendMessage(GetNativeView(), WM_NCHITTEST, 0, MAKELPARAM(pt.x, pt.y));
+    if (ht_component == HTCAPTION || ht_component == HTSYSMENU) {
+      RunSystemMenu(gfx::Point(pt));
+      return;
+    }
+  }
+
+  WidgetWin::OnRButtonUp(ht_component, point);
 }
 
 LRESULT WindowWin::OnNCUAHDrawCaption(UINT msg, WPARAM w_param,
                                       LPARAM l_param) {
   // See comment in widget_win.h at the definition of WM_NCUAHDRAWCAPTION for
   // an explanation about why we need to handle this message.
   SetMsgHandled(!non_client_view_->UseNativeFrame());
   return 0;
 }
 
@@ skipping 432 matching lines @@
   }
   return TRUE;
 }
 }  // namespace
 
 void Window::CloseAllSecondaryWindows() {
   EnumThreadWindows(GetCurrentThreadId(), WindowCallbackProc, 0);
 }
 
 }  // namespace views