[Win] Only update HWND styles on SizeConstraintsChanged for normal wi…

…ndows.

An earlier CL added SizeConstraintsChanged which updates the HWND's
style flags: https://codereview.chromium.org/581953002/

To be consistent with CalculateWindowStylesFromInitParams in
widget_hwnd_utils, it should only set the style on normal windows.

BUG=417986

Review URL: https://codereview.chromium.org/611223002

Cr-Commit-Position: refs/heads/master@{#297582}

ui/views/win/hwnd_message_handler.cc

@@ -870,6 +870,10 @@ void HWNDMessageHandler::SetFullscreen(bool fullscreen) {
 
 void HWNDMessageHandler::SizeConstraintsChanged() {
   LONG style = GetWindowLong(hwnd(), GWL_STYLE);
+  // Ignore if this is not a standard window.
+  if (!(style & WS_OVERLAPPED))
+    return;
+
   if (delegate_->CanResize()) {
     style |= WS_THICKFRAME | WS_MAXIMIZEBOX;
     if (!delegate_->CanMaximize())