Proper fix for accessibility in Windows 64 build.

content/browser/renderer_host/legacy_render_widget_host_win.cc

 // 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.
 
 #include "content/browser/renderer_host/legacy_render_widget_host_win.h"
 
 #include "base/command_line.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/win/windows_version.h"
 #include "content/browser/accessibility/browser_accessibility_manager_win.h"
 #include "content/browser/accessibility/browser_accessibility_win.h"
 #include "content/public/browser/browser_accessibility_state.h"
 #include "content/public/common/content_switches.h"
 #include "ui/base/touch/touch_enabled.h"
 #include "ui/base/view_prop.h"
 #include "ui/base/win/internal_constants.h"
 #include "ui/base/win/window_event_target.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace content {
 
 // A custom MSAA object id used to determine if a screen reader or some
 // other client is listening on MSAA events - if so, we enable full web
 // accessibility support.
 const int kIdScreenReaderHoneyPot = 1;
 
-// A version of the OBJID_CLIENT constant that works in 64-bit mode too.
-static const LPARAM kObjIdClient = static_cast<ULONG>(OBJID_CLIENT);
-
 LegacyRenderWidgetHostHWND::~LegacyRenderWidgetHostHWND() {
   ::DestroyWindow(hwnd());
 }
 
 // static
 scoped_ptr<LegacyRenderWidgetHostHWND> LegacyRenderWidgetHostHWND::Create(
     HWND parent) {
   // content_unittests passes in the desktop window as the parent. We allow
   // the LegacyRenderWidgetHostHWND instance to be created in this case for
   // these tests to pass.
@@ skipping 89 matching lines @@
 
 LRESULT LegacyRenderWidgetHostHWND::OnEraseBkGnd(UINT message,
                                                  WPARAM w_param,
                                                  LPARAM l_param) {
   return 1;
 }
 
 LRESULT LegacyRenderWidgetHostHWND::OnGetObject(UINT message,
                                                 WPARAM w_param,
                                                 LPARAM l_param) {
-  if (kIdScreenReaderHoneyPot == l_param) {
+  // Only the lower 32 bits of l_param are valid when checking the object id
+  // because it sometimes gets sign-extended incorrectly (but not always).
+  DWORD_PTR unsigned_l_param = static_cast<DWORD_PTR>(l_param);
+  DWORD obj_id = static_cast<DWORD>(unsigned_l_param);

[jschuh, 2014/06/19 09:15:19]

I'd just stack the casts like this (we do the same elsewhere):

DWORD obj_id = static_cast<DWORD>(static_cast<DWORD_PTR>(l_param));

+
+  if (kIdScreenReaderHoneyPot == obj_id) {
     // When an MSAA client has responded to our fake event on this id,
     // enable screen reader support.
     BrowserAccessibilityState::GetInstance()->OnScreenReaderDetected();
     return static_cast<LRESULT>(0L);
   }
 
-  if (kObjIdClient != l_param || !manager_)
+  if (OBJID_CLIENT != obj_id || !manager_)
     return static_cast<LRESULT>(0L);
 
   base::win::ScopedComPtr<IAccessible> root(
       manager_->GetRoot()->ToBrowserAccessibilityWin());
   return LresultFromObject(IID_IAccessible, w_param,
       static_cast<IAccessible*>(root.Detach()));
 }
 
 // We send keyboard/mouse/touch messages to the parent window via SendMessage.
 // While this works, this has the side effect of converting input messages into
@@ skipping 164 matching lines @@
   // generate the legacy WM_VSCROLL/WM_HSCROLL messages.
   // We add these styles to ensure that trackpad/trackpoint scrolling
   // work.
   long current_style = ::GetWindowLong(hwnd(), GWL_STYLE);
   ::SetWindowLong(hwnd(), GWL_STYLE,
                   current_style | WS_VSCROLL | WS_HSCROLL);
   return 0;
 }
 
 }  // namespace content