Remove usage of X11AtomCache

See https://codereview.chromium.org/2914103002/

atom/browser/ui/x/window_state_watcher.cc

@@ -7,6 +7,7 @@
 #include <X11/Xlib.h>
 
 #include "ui/events/platform/platform_event_source.h"
+#include "ui/gfx/x/x11_atom_cache.h"
 
 namespace atom {
 
@@ -22,7 +23,6 @@ const char* kAtomsToCache[] = {
 WindowStateWatcher::WindowStateWatcher(NativeWindowViews* window)
     : window_(window),
       widget_(window->GetAcceleratedWidget()),
-      atom_cache_(gfx::GetXDisplay(), kAtomsToCache),
       was_minimized_(false),
       was_maximized_(false) {
   ui::PlatformEventSource::GetInstance()->AddPlatformEventObserver(this);
@@ -70,7 +70,7 @@ void WindowStateWatcher::DidProcessEvent(const ui::PlatformEvent& event) {
 
 bool WindowStateWatcher::IsWindowStateEvent(const ui::PlatformEvent& event) {
   ::Atom changed_atom = event->xproperty.atom;
-  return (changed_atom == atom_cache_.GetAtom("_NET_WM_STATE") &&
+  return (changed_atom == gfx::GetAtom("_NET_WM_STATE") &&
           event->type == PropertyNotify &&
           event->xproperty.window == widget_);
 }

atom/browser/ui/x/window_state_watcher.h

@@ -8,7 +8,6 @@
 #include "ui/events/platform/platform_event_observer.h"
 
 #include "atom/browser/native_window_views.h"
-#include "ui/gfx/x/x11_atom_cache.h"
 
 namespace atom {
 
@@ -28,8 +27,6 @@ class WindowStateWatcher : public ui::PlatformEventObserver {
   NativeWindowViews* window_;
   gfx::AcceleratedWidget widget_;
 
-  ui::X11AtomCache atom_cache_;
-
   bool was_minimized_;
   bool was_maximized_;