Fix a long standing bug with the browser window losing focus when the user scrolled on the page usi…

ui/views/win/hwnd_message_handler.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/win/hwnd_message_handler.h"
 
 #include <dwmapi.h>
 #include <oleacc.h>
 #include <shellapi.h>
 #include <wtsapi32.h>
@@ skipping 1531 matching lines @@
   // WM_MOUSEACTIVATE handler and don't activate the window if the property is
   // set.
   if (::GetProp(hwnd(), ui::kIgnoreTouchMouseActivateForWindow)) {
     ::RemoveProp(hwnd(), ui::kIgnoreTouchMouseActivateForWindow);
     return MA_NOACTIVATE;
   }
   // A child window activation should be treated as if we lost activation.
   POINT cursor_pos = {0};
   ::GetCursorPos(&cursor_pos);
   ::ScreenToClient(hwnd(), &cursor_pos);
+  // The code below exists for child windows like NPAPI plugins etc which need
+  // to be activated whenever we receive a WM_MOUSEACTIVATE message. Don't put
+  // transparent child windows in this bucket as they are not supposed to grab
+  // activation.
+  // TODO(ananta)
+  // Get rid of this code when we deprecate NPAPI plugins.
   HWND child = ::RealChildWindowFromPoint(hwnd(), cursor_pos);
-  if (::IsWindow(child) && child != hwnd() && ::IsWindowVisible(child))
+  if (::IsWindow(child) && child != hwnd() && ::IsWindowVisible(child) &&
+      !(::GetWindowLong(child, GWL_EXSTYLE) & WS_EX_TRANSPARENT))
     PostProcessActivateMessage(WA_INACTIVE, false);
 
   // TODO(beng): resolve this with the GetWindowLong() check on the subsequent
   //             line.
   if (delegate_->IsWidgetWindow())
     return delegate_->CanActivate() ? MA_ACTIVATE : MA_NOACTIVATEANDEAT;
   if (GetWindowLong(hwnd(), GWL_EXSTYLE) & WS_EX_NOACTIVATE)
     return MA_NOACTIVATE;
   SetMsgHandled(FALSE);
   return MA_ACTIVATE;
@@ skipping 921 matching lines @@
     SetWindowPos(hwnd(), NULL, 0, 0, 0, 0, flags | SWP_HIDEWINDOW);
     SetWindowPos(hwnd(), NULL, 0, 0, 0, 0, flags | SWP_SHOWWINDOW);
   }
   // WM_DWMCOMPOSITIONCHANGED is only sent to top level windows, however we want
   // to notify our children too, since we can have MDI child windows who need to
   // update their appearance.
   EnumChildWindows(hwnd(), &SendDwmCompositionChanged, NULL);
 }
 
 }  // namespace views