Don't check autohide taskbar for WS_EX_TOPMOST when we are querying the autohide state.

ui/views/win/hwnd_message_handler.cc

Index: ui/views/win/hwnd_message_handler.cc
diff --git a/ui/views/win/hwnd_message_handler.cc b/ui/views/win/hwnd_message_handler.cc
index 6f80d3e568e2ca1dc1471d563356f850ec2bdc39..2a770d17a2449feca470a80103b8cb32eff0fbfd 100644
--- a/ui/views/win/hwnd_message_handler.cc
+++ b/ui/views/win/hwnd_message_handler.cc
@@ -376,6 +376,13 @@ void HWNDMessageHandler::Init(HWND parent, const gfx::Rect& bounds) {
 
   // Disable pen flicks (http://crbug.com/506977)
   base::win::DisableFlicks(hwnd());
+
+  // Register for fullscreen window notifications from the shell.
+  APPBARDATA appbar = {};
+  appbar.cbSize = sizeof(APPBARDATA);
+  appbar.hWnd = hwnd();
+  appbar.uCallbackMessage = WM_APPBAR_NOTIFICATION_MESSAGE;
+  ::SHAppBarMessage(ABM_NEW, &appbar);
 }
 
 void HWNDMessageHandler::InitModalType(ui::ModalType modal_type) {
@@ -418,6 +425,12 @@ void HWNDMessageHandler::Close() {
 }
 
 void HWNDMessageHandler::CloseNow() {
+  // Unregister fullscreen notifications from the shell.
+  APPBARDATA appbar = {};
+  appbar.cbSize = sizeof(APPBARDATA);
+  appbar.hWnd = hwnd();
+  ::SHAppBarMessage(ABM_REMOVE, &appbar);
+
   // We may already have been destroyed if the selection resulted in a tab
   // switch which will have reactivated the browser window and closed us, so
   // we need to check to see if we're still a window before trying to destroy
@@ -2387,6 +2400,24 @@ LRESULT HWNDMessageHandler::OnWindowSizingFinished(UINT message,
   return 0;
 }
 
+LRESULT HWNDMessageHandler::OnAppBarMessage(UINT message,
+                                            WPARAM w_param,
+                                            LPARAM l_param) {
+  // Please refer to the ChromeViewsDelegate::GetAppbarAutohideEdges() function
+  // for some context on how we handle autohide taskbars.
+
+  // We receive this notification when a window changes from fullscreen to
+  // non fullscreen. Sadly we don't get the window handle. The problem we
+  // are trying to address is the case where our window switched away to
+  // maximized from fullscreen mode and the autohide taskbar is around.
+  // We want to leave a pixel space at the place where the taskbar shows up
+  // to ensure that the taskbar shows up when the mouse is moved there.
+  // The SendFrameChanged() call below achieves that.
+  if (w_param == ABN_FULLSCREENAPP && (l_param == 0) && IsMaximized())
+    SendFrameChanged();

[Peter Kasting, 2016/12/02 01:56:41]

Now that we removed the TOPMOST check, does this still have any effect?

It seems like it would have an effect if, while Chrome was fullscreened, an app
bar would be missing entirely, or in a different position, than when not
fullscreened, from the perspective of ABM_GETAUTOHIDEBAR/ABM_GETTASKBARPOS (i.e.
the checking code in MonitorHasAutohideTaskbarForEdge()).  In that case, we'd
want to make sure we check the autohide state after we come out of fullscreen
mode.  But is that the case with the TOPMOST removal?  It seems like
fullscreening should just change appbar z-order, not affect the results of those
two functions, which means this shouldn't actually matter.

(If it did matter, it seems like a better fix than asking the shell for
notifications here would be modifying views/aura itself to do this notification
once we're sufficiently out of fullscreen mode.)

[ananta, 2016/12/02 06:09:14]

I added this mostly for correctness sake, i.e querying the autohide state when
the taskbar says that a fullscreen window has gone away which is the case we
generally struggle with.

However you are right that with the TOPMOST check removal this is just
superficial. I will revert this part of the change.

+  return 0;
+}
+
 void HWNDMessageHandler::OnSessionChange(WPARAM status_code) {
   // Direct3D presents are ignored while the screen is locked, so force the
   // window to be redrawn on unlock.