Adds a class that makes it easy to subclass a HWND and filter messages sent to it.

ui/views/widget/hwnd_subclass.cc

+// Copyright (c) 2012 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 "ui/views/widget/hwnd_subclass.h"
+
+#include "base/logging.h"
+#include "ui/base/win/hwnd_util.h"
+
+namespace {
+const char* kHWNDSubclassKey = "__VIEWS_HWND_SUBCLASS_PROC__";
+
+LRESULT CALLBACK WndProc(HWND hwnd,
+                         UINT message,
+                         WPARAM w_param,
+                         LPARAM l_param) {
+  views::HWNDSubclass* wrapped_wnd_proc =
+      reinterpret_cast<views::HWNDSubclass*>(
+          ui::ViewProp::GetValue(hwnd, kHWNDSubclassKey));
+  return wrapped_wnd_proc ? wrapped_wnd_proc->OnWndProc(hwnd,
+                                                        message,
+                                                        w_param,
+                                                        l_param) : 0;

[cpu_(ooo_6.6-7.5), 2012/04/27 20:20:25]

why return 0 instead of CallWindowProc?

+}
+
+}
+
+namespace views {
+
+HWNDSubclass::HWNDSubclass(gfx::AcceleratedWidget target)

[cpu_(ooo_6.6-7.5), 2012/04/27 20:20:25]

so a gfx::AcceleatedWidget is a hwnd? in the h file the declaration is explicit
HWNDSubclass(HWND target);

+    : target_(target),
+      original_wnd_proc_(GetClassWndProc(target)),

[cpu_(ooo_6.6-7.5), 2012/04/27 20:20:25]

but the window could be already be subclassed...

+      ALLOW_THIS_IN_INITIALIZER_LIST(prop_(target, kHWNDSubclassKey, this)) {
+  ui::SetWindowProc(target_, &WndProc);
+}
+
+HWNDSubclass::~HWNDSubclass() {
+  // This is important, since otherwise we will try to access this object again
+  // via a destroyed ViewProp.
+  ui::SetWindowProc(target_, original_wnd_proc_);

[cpu_(ooo_6.6-7.5), 2012/04/27 20:20:25]

I wont't bother unsubclassing, see my comment of line 23. I could be subclassed
again.

+}
+
+LRESULT HWNDSubclass::OnWndProc(HWND hwnd,
+                                UINT message,
+                                WPARAM w_param,
+                                LPARAM l_param) {
+  LRESULT l_result = 0;
+  bool consumed = FilterMessage(hwnd, message, w_param, l_param, &l_result);
+  if (consumed)
+    return l_result;
+
+  // In most cases, |original_wnd_proc_| will take care of calling
+  // DefWindowProc.
+  return CallWindowProc(original_wnd_proc_, hwnd, message, w_param, l_param);
+}
+
+bool HWNDSubclass::FilterMessage(HWND hwnd,
+                                 UINT message,
+                                 WPARAM w_param,
+                                 LPARAM l_param,
+                                 LRESULT* l_result) {
+  return false;
+}
+
+// static
+WNDPROC HWNDSubclass::GetClassWndProc(HWND target) {
+  wchar_t class_name[MAX_PATH];
+  ::GetClassName(target, class_name, MAX_PATH);
+
+  WNDCLASSEX wndclassex = {0};
+  wndclassex.cbSize = sizeof(wndclassex);
+  GetClassInfoEx(GetModuleHandle(NULL), class_name, &wndclassex);
+  return wndclassex.lpfnWndProc;
+}
+
+// static
+WNDPROC HWNDSubclass::GetCurrentWndProc(HWND target) {
+  return reinterpret_cast<WNDPROC>(GetWindowLong(target, GWL_WNDPROC));

[cpu_(ooo_6.6-7.5), 2012/04/27 20:20:25]

are we using this function?

+}
+
+}  // namespace views