3 files changed, 113 insertions, 0 deletions
diff --git a/app/active_window_watcher_x.cc b/app/active_window_watcher_x.cc
new file mode 100644
index 0000000..d834a5c
--- /dev/null
+++ b/app/active_window_watcher_x.cc
@@ -0,0 +1,63 @@
+// Copyright (c) 2009 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 <X11/Xlib.h>
+#include <gdk/gdk.h>
+#include <gdk/gdkx.h>
+
+#include "app/active_window_watcher_x.h"
+
+// static
+void ActiveWindowWatcherX::AddObserver(Observer* observer) {
+  Singleton<ActiveWindowWatcherX>::get()->observers_.AddObserver(observer);
+}
+
+// static
+void ActiveWindowWatcherX::RemoveObserver(Observer* observer) {
+  Singleton<ActiveWindowWatcherX>::get()->observers_.RemoveObserver(observer);
+}
+
+ActiveWindowWatcherX::ActiveWindowWatcherX() {
+  Init();
+}
+
+void ActiveWindowWatcherX::Init() {
+  // Set up X Event filter to listen for PropertyChange X events.  These events
+  // tell us when the active window changes.
+  GdkWindow* root = gdk_screen_get_root_window(gdk_screen_get_default());
+  gdk_window_add_filter(root, &ActiveWindowWatcherX::OnWindowXEvent, this);
+  XSelectInput(GDK_WINDOW_XDISPLAY(root), GDK_WINDOW_XID(root),
+               PropertyChangeMask);
+}
+
+void ActiveWindowWatcherX::NotifyActiveWindowChanged() {
+  GdkWindow* active_window = gdk_screen_get_active_window(
+      gdk_screen_get_default());
+
+  // If the window manager doesn't support _NET_ACTIVE_WINDOW, we don't know
+  // which window is active and just give up.
+  if (!active_window)
+    return;
+
+  FOR_EACH_OBSERVER(Observer, observers_, ActiveWindowChanged(active_window));
+}
+
+GdkFilterReturn ActiveWindowWatcherX::OnWindowXEvent(GdkXEvent* xevent,
+    GdkEvent* event, gpointer window_watcher) {
+  static const GdkAtom kNetActiveWindow = gdk_atom_intern(
+      "_NET_ACTIVE_WINDOW", FALSE);
+  static const Atom kNetActiveWindowAtom = gdk_x11_atom_to_xatom_for_display(
+        gdk_screen_get_display(gdk_screen_get_default()), kNetActiveWindow);
+
+  ActiveWindowWatcherX* watcher = reinterpret_cast<ActiveWindowWatcherX*>(
+      window_watcher);
+  XEvent* xev = static_cast<XEvent*>(xevent);
+
+  if (xev->xany.type == PropertyNotify &&
+      xev->xproperty.atom == kNetActiveWindowAtom) {
+    watcher->NotifyActiveWindowChanged();
+  }
+
+  return GDK_FILTER_CONTINUE;
+}
diff --git a/app/active_window_watcher_x.h b/app/active_window_watcher_x.h
new file mode 100644
index 0000000..2ea524e
--- /dev/null
+++ b/app/active_window_watcher_x.h
@@ -0,0 +1,48 @@
+// Copyright (c) 2009 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.
+
+#ifndef APP_ACTIVE_WINDOW_WATCHER_X_H_
+#define APP_ACTIVE_WINDOW_WATCHER_X_H_
+
+#include <gdk/gdk.h>
+
+#include "base/basictypes.h"
+#include "base/observer_list.h"
+#include "base/singleton.h"
+
+// This is a helper class that is used to keep track of which window the X
+// window manager thinks is active. Add an Observer to listener for changes to
+// the active window.
+class ActiveWindowWatcherX {
+ public:
+  class Observer {
+   public:
+    virtual void ActiveWindowChanged(GdkWindow* active_window) = 0;
+  };
+
+  static void AddObserver(Observer* observer);
+  static void RemoveObserver(Observer* observer);
+
+ private:
+  friend struct DefaultSingletonTraits<ActiveWindowWatcherX>;
+
+  ActiveWindowWatcherX();
+
+  void Init();
+
+  // Sends a notification out through the NotificationService that the active
+  // window has changed.
+  void NotifyActiveWindowChanged();
+
+  // Callback for PropertyChange XEvents.
+  static GdkFilterReturn OnWindowXEvent(GdkXEvent* xevent,
+                                        GdkEvent* event,
+                                        gpointer window_watcher);
+
+  ObserverList<Observer> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ActiveWindowWatcherX);
+};
+
+#endif  // APP_ACTIVE_WINDOW_WATCHER_X_H_
diff --git a/app/app.gyp b/app/app.gyp
index 7c61d17..73d65ba 100644
--- a/app/app.gyp
+++ b/app/app.gyp
@@ -59,6 +59,8 @@
         # All .cc, .h, and .mm files under app/ except for tests.
         'animation.cc',
         'animation.h',
+        'active_window_watcher_x.cc',
+        'active_window_watcher_x.h',
         'app_paths.h',
         'app_paths.cc',
         'app_switches.h',