[ozone/x11] Implement HasCapture method

When user clicks on a non client area, the content
area stops receiving events because base implementation
of the HasCapture method always returns false. This
confuses the capture client, and capture is never
reset.

Thus, to fix the problem, implement the method on
the X11WindowOzone level and provide up-to-date
information whether the window has explicit capture
or not.

Bug: 789065
Change-Id: I4445f4cceb7c801f0ab0cfe4df005e977ba36569
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1657829Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/master@{#669142}

ui/ozone/platform/x11/x11_window_ozone.cc

@@ -44,6 +44,10 @@ void X11WindowOzone::ReleaseCapture() {
   window_manager_->UngrabEvents(this);
 }
 
+bool X11WindowOzone::HasCapture() const {
+  return window_manager_->event_grabber() == this;
+}
+
 void X11WindowOzone::SetCursor(PlatformCursor cursor) {
   X11CursorOzone* cursor_ozone = static_cast<X11CursorOzone*>(cursor);
   XDefineCursor(xdisplay(), xwindow(), cursor_ozone->xcursor());

ui/ozone/platform/x11/x11_window_ozone.h

@@ -31,6 +31,7 @@ class X11WindowOzone : public X11WindowBase,
   void PrepareForShutdown() override;
   void SetCapture() override;
   void ReleaseCapture() override;
+  bool HasCapture() const override;
   void SetCursor(PlatformCursor cursor) override;
 
   // XEventDispatcher: