Focus manager subclassing check

chrome/views/focus_manager.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 <algorithm>
 
+#include "base/histogram.h"
 #include "base/logging.h"
 #include "base/win_util.h"
 #include "chrome/browser/render_widget_host_view_win.h"
 #include "chrome/common/notification_types.h"
 #include "chrome/views/accelerator.h"
 #include "chrome/views/focus_manager.h"
 #include "chrome/views/root_view.h"
 #include "chrome/views/view.h"
 #include "chrome/views/view_storage.h"
 #include "chrome/views/widget.h"
 
 // The following keys are used in SetProp/GetProp to associate additional
 // information needed for focus tracking with a window.
 
 // Maps to the FocusManager instance for a top level window. See
 // CreateFocusManager/DestoryFocusManager for usage.
 static const wchar_t* const kFocusManagerKey = L"__VIEW_CONTAINER__";
 
 // Maps to the View associated with a window.
 // We register views with window so we can:
 // - keep in sync the native focus with the view focus (when the native
 //   component gets the focus, we get the WM_SETFOCUS event and we can focus the
 //   associated view).
 // - prevent tab key events from being sent to views.
 static const wchar_t* const kViewKey = L"__CHROME_VIEW__";
 
+// A property set to 1 to indicate whether the focus manager has subclassed that
+// window.  We are doing this to ensure we are not subclassing several times.
+// Subclassing twice is not a problem if no one is subclassing the HWND between
+// the 2 subclassing (the 2 subclassing is ignored since the WinProc is the same
+// as the current one).  However if some other app goes and subclasses the HWND
+// between the 2 subclassing, we will end up subclassing twice.
+// This flag lets us test that whether we have or not subclassed yet.
+static const wchar_t* const kSubclassed = L"__FOCUS_SUBCLASS_INSTALLED__";
+
 namespace views {
 
 static bool IsCompatibleWithMouseWheelRedirection(HWND window) {
   std::wstring class_name = win_util::GetClassName(window);
   // Mousewheel redirection to comboboxes is a surprising and
   // undesireable user behavior.
   return !(class_name == L"ComboBox" ||
            class_name == L"ComboBoxEx32");
 }
 
@@ skipping 159 matching lines @@
   // keep references to invalidated views.
   NotificationService::current()->AddObserver(
       focus_manager, NOTIFY_VIEW_REMOVED, NotificationService::AllSources());
 
   return focus_manager;
 }
 
 // static
 void FocusManager::InstallFocusSubclass(HWND window, View* view) {
   DCHECK(window);
-  win_util::Subclass(window, &FocusWindowCallback);
+
+  bool already_subclassed =  reinterpret_cast<bool>(GetProp(window,
+                                                            kSubclassed));
+  if (already_subclassed &&
+      !win_util::IsSubclassed(window, &FocusWindowCallback)) {
+    NOTREACHED() << " FocusManager sub-classed twice";
+    // Track in UMA so we know if this case happens.
+    UMA_HISTOGRAM_COUNTS(L"FocusManager.MultipleSubclass", 1);
+  } else {
+    bool success = win_util::Subclass(window, &FocusWindowCallback);
+    DCHECK(success);
+    SetProp(window, kSubclassed, reinterpret_cast<HANDLE>(true));
+  }
   if (view)
     SetProp(window, kViewKey, view);
 }
 
 void FocusManager::UninstallFocusSubclass(HWND window) {
   DCHECK(window);
-  if (win_util::Unsubclass(window, &FocusWindowCallback))
+  if (win_util::Unsubclass(window, &FocusWindowCallback)) {
     RemoveProp(window, kViewKey);
+    RemoveProp(window, kSubclassed);
+  }
 }
 
 // static
 FocusManager* FocusManager::GetFocusManager(HWND window) {
   DCHECK(window);
   FocusManager* focus_manager =
         reinterpret_cast<FocusManager*>(GetProp(window, kFocusManagerKey));
   HWND parent = GetParent(window);
   while (!focus_manager && parent) {
     focus_manager =
@@ skipping 572 matching lines @@
                 listener);
   if (place == focus_change_listeners_.end()) {
     NOTREACHED() << "Removing a listener that isn't registered.";
     return;
   }
   focus_change_listeners_.erase(place);
 }
 
 }  // namespace views