Restore maximized window position after detaching display.

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 ec631af3b840741db1404d454ad652586b11bc25..1159db0656c03bbec4b7e576b8b2ddbef90dde0d 100644
--- a/ui/views/win/hwnd_message_handler.cc
+++ b/ui/views/win/hwnd_message_handler.cc
@@ -2230,6 +2230,27 @@ void HWNDMessageHandler::OnWindowPosChanging(WINDOWPOS* window_pos) {
         GetMonitorAndRects(window_rect, &monitor, &monitor_rect, &work_area)) {
       bool work_area_changed = (monitor_rect == last_monitor_rect_) &&
                                (work_area != last_work_area_);
+      const bool same_monitor = monitor && (monitor == last_monitor_);

[ananta, 2016/10/06 19:59:57]

If a monitor is attached or detached, do we get a WM_DISPLAYCHANGE message?. If
yes, then it seems better to do this part in that handler. Reason being, this
function has already many edge cases which makes it a nightmare to debug
problems.

[atimoxin, 2016/10/07 15:27:22]

Yes, we get this message, but we get it before the system tries to change
window's bounds, so we can't fix bounds here.

I logged related messages (using this patch:
https://gist.github.com/anonymous/b62416dc29fcbb7e7ae2b7cb1a6ba9c0) and have got
this result with my hack:
https://gist.github.com/anonymous/9d508fe5e94652c1a9610e431a03937b
and this when hack is disabled:
https://gist.github.com/anonymous/9de27864177f9d4378dcb17e29f744e7

+
+      gfx::Rect expected_maximized_bounds = work_area;
+      if (IsMaximized()) {
+        // Windows automatically adds a standard width border to all sides when
+        // window is maximized. We should take this into account.
+        gfx::Insets client_area_insets;
+        if (GetClientAreaInsets(&client_area_insets))
+          expected_maximized_bounds.Inset(client_area_insets.Scale(-1));
+      }
+      // Sometimes Windows incorrectly changes bounds of maximized windows after
+      // attaching or detaching additional displays. In this case user can see
+      // non-client area of the window (that should be hidden in normal case).
+      // We should restore window position if problem occurs.
+      const bool incorrect_maximized_bounds =
+          IsMaximized() &&
+          (expected_maximized_bounds.x() != window_pos->x ||
+           expected_maximized_bounds.y() != window_pos->y ||
+           expected_maximized_bounds.width() != window_pos->cx ||
+           expected_maximized_bounds.height() != window_pos->cy);
+
       // If the size of a background fullscreen window changes again, then we
       // should reset the |background_fullscreen_hack_| flag.
       if (background_fullscreen_hack_ &&
@@ -2237,9 +2258,11 @@ void HWNDMessageHandler::OnWindowPosChanging(WINDOWPOS* window_pos) {
             (monitor_rect.height() - window_pos->cy != 1))) {
           background_fullscreen_hack_ = false;
       }
-      if (monitor && (monitor == last_monitor_) &&
-          ((IsFullscreen() && !background_fullscreen_hack_) ||
-           work_area_changed)) {
+      const bool fullscreen_without_hack =
+          IsFullscreen() && !background_fullscreen_hack_;
+
+      if (incorrect_maximized_bounds ||
+          (same_monitor && (fullscreen_without_hack || work_area_changed))) {
         // A rect for the monitor we're on changed.  Normally Windows notifies
         // us about this (and thus we're reaching here due to the SetWindowPos()
         // call in OnSettingChange() above), but with some software (e.g.
@@ -2252,9 +2275,7 @@ void HWNDMessageHandler::OnWindowPosChanging(WINDOWPOS* window_pos) {
         if (IsFullscreen()) {
           new_window_rect = monitor_rect;
         } else if (IsMaximized()) {
-          new_window_rect = work_area;
-          int border_thickness = GetSystemMetrics(SM_CXSIZEFRAME);
-          new_window_rect.Inset(-border_thickness, -border_thickness);
+          new_window_rect = expected_maximized_bounds;
         } else {
           new_window_rect = gfx::Rect(window_rect);
           new_window_rect.AdjustToFit(work_area);