Clear root window when the aura root window is moved/resized

ui/aura/root_window_host_linux.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/root_window_host_linux.h"
 
 #include <X11/cursorfont.h>
 #include <X11/extensions/Xfixes.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/extensions/Xrandr.h>
@@ skipping 493 matching lines @@
             p.SetPoint(0, 0);
           XWarpPointer(
               xdisplay_, None, x_root_window_, 0, 0, 0, 0, p.x(), p.y());
         }
         ConfineCursorToRootWindow();
       }
       if (size_changed)
         delegate_->OnHostResized(bounds.size());
       if (origin_changed)
         delegate_->OnHostMoved(bounds_.origin());
+#if defined(OS_CHROMEOS)
+      // TODO(oshima): Clear the root when the window is moved or
+      // resized while the extended desktop is disabled.
+      // crbug.com/152003.
+      if (base::chromeos::IsRunningOnChromeOS()) {
+        XGCValues gc_values = {0};
+        gc_values.foreground = BlackPixel(xdisplay_, DefaultScreen(xdisplay_));
+        GC gc = XCreateGC(xdisplay_, x_root_window_, GCForeground, &gc_values);
+        XFillRectangle(xdisplay_, x_root_window_, gc,
+                       x_root_bounds_.x(),
+                       x_root_bounds_.y(),
+                       x_root_bounds_.width(),
+                       x_root_bounds_.height());
+        XFreeGC(xdisplay_, gc);
+      }
+#endif
       break;
     }
     case GenericEvent:
       DispatchXI2Event(event);
       break;
     case MapNotify: {
       // If there's no window manager running, we need to assign the X input
       // focus to our host window.
       if (!IsWindowManagerPresent() && focus_when_shown_)
         XSetInputFocus(xdisplay_, xwindow_, RevertToNone, CurrentTime);
@@ skipping 495 matching lines @@
       ui::ViewProp::GetValue(accelerated_widget, kRootWindowHostLinuxKey));
 }
 
 // static
 gfx::Size RootWindowHost::GetNativeScreenSize() {
   ::Display* xdisplay = base::MessagePumpAuraX11::GetDefaultXDisplay();
   return gfx::Size(DisplayWidth(xdisplay, 0), DisplayHeight(xdisplay, 0));
 }
 
 }  // namespace aura