Stop removing WS_THICKFRAME style on full screen.

Also, change IsFullScreenWindowMode to not require the absence of
WS_THICKFRAME when deciding if a window is full screen.

This issue this fixes involves the glass_browser_frame_view when
maximizing after going full screen - an extra 8 pixel bar gets drawn
above a maximized window, and if there's another monitor
above the one with chrome maximized, the bar gets drawn on
the other monitor.

Windows doc
 https://docs.microsoft.com/en-us/windows/win32/winmsg/window-styles
claims that some styles can't be changed after the window is
created, but also says that if you change frame styles, you
need to call SetWindowPos with SWP_FRAMECHANGED, which we are doing.

Not removing the WS_THICKFRAME style doesn't seem to have any visible
effect on full screen windows.

Bug: 1014720
Change-Id: Ibfbd480c603fd7c3aca74081201e99e59fbbbecc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1972258Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791237}

ui/base/fullscreen_win.cc

@@ -47,11 +47,11 @@ bool IsFullScreenWindowMode() {
   if (!::EqualRect(&wnd_rect, &monitor_info.rcMonitor))
     return false;
 
-  // At last, the window style should not have WS_DLGFRAME and WS_THICKFRAME and
-  // its extended style should not have WS_EX_WINDOWEDGE and WS_EX_TOOLWINDOW.
+  // At last, the window style should not have WS_DLGFRAME and its extended
+  // style should not have WS_EX_WINDOWEDGE and WS_EX_TOOLWINDOW.
   LONG style = ::GetWindowLong(wnd, GWL_STYLE);
   LONG ext_style = ::GetWindowLong(wnd, GWL_EXSTYLE);
-  return !((style & (WS_DLGFRAME | WS_THICKFRAME)) ||
+  return !((style & WS_DLGFRAME) ||
            (ext_style & (WS_EX_WINDOWEDGE | WS_EX_TOOLWINDOW)));
 }
 

ui/views/win/fullscreen_handler.cc

@@ -72,8 +72,7 @@ void FullscreenHandler::SetFullscreenImpl(bool fullscreen) {
 
   if (fullscreen_) {
     // Set new window style and size.
-    SetWindowLong(hwnd_, GWL_STYLE,
-                  saved_window_info_.style & ~(WS_CAPTION | WS_THICKFRAME));
+    SetWindowLong(hwnd_, GWL_STYLE, saved_window_info_.style & ~WS_CAPTION);
     SetWindowLong(
         hwnd_, GWL_EXSTYLE,
         saved_window_info_.ex_style & ~(WS_EX_DLGMODALFRAME | WS_EX_WINDOWEDGE |