5 files changed, 48 insertions, 13 deletions
diff --git a/base/message_loop.h b/base/message_loop.h
index a64196ce..c747947 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -80,12 +80,11 @@ class BASE_API MessageLoop : public base::MessagePump::Delegate {
 #if defined(OS_WIN)
   typedef base::MessagePumpWin::Dispatcher Dispatcher;
   typedef base::MessagePumpForUI::Observer Observer;
-#elif !defined(OS_MACOSX)
-#if defined(TOUCH_UI)
+#elif defined(TOUCH_UI)
   typedef base::MessagePumpGlibXDispatcher Dispatcher;
-#else
+  typedef base::MessagePumpXObserver Observer;
+#elif !defined(OS_MACOSX)
   typedef base::MessagePumpForUI::Dispatcher Dispatcher;
-#endif
   typedef base::MessagePumpForUI::Observer Observer;
 #endif
 
diff --git a/base/message_pump_glib.h b/base/message_pump_glib.h
index 7d7d8da..32d0d8f 100644
--- a/base/message_pump_glib.h
+++ b/base/message_pump_glib.h
@@ -93,6 +93,8 @@ class MessagePumpForUI : public MessagePump {
   // Returns the dispatcher for the current run state (|state_->dispatcher|).
   Dispatcher* GetDispatcher();
 
+  ObserverList<Observer>& observers() { return observers_; }
+
  private:
   // We may make recursive calls to Run, so we save state that needs to be
   // separate between them in this structure type.
diff --git a/base/message_pump_glib_x.cc b/base/message_pump_glib_x.cc
index dcb3e2c..b4d677e 100644
--- a/base/message_pump_glib_x.cc
+++ b/base/message_pump_glib_x.cc
@@ -70,15 +70,17 @@ bool MessagePumpGlibX::RunOnce(GMainContext* context, bool block) {
       }
 #endif
 
-      MessagePumpGlibXDispatcher::DispatchStatus status =
-          static_cast<MessagePumpGlibXDispatcher*>
-          (GetDispatcher())->DispatchX(&xev);
-
-      if (status == MessagePumpGlibXDispatcher::EVENT_QUIT) {
-        should_quit = true;
-        Quit();
-      } else if (status == MessagePumpGlibXDispatcher::EVENT_IGNORED) {
-        DLOG(WARNING) << "Event (" << xev.type << ") not handled.";
+      if (!WillProcessXEvent(&xev)) {
+        MessagePumpGlibXDispatcher::DispatchStatus status =
+            static_cast<MessagePumpGlibXDispatcher*>
+            (GetDispatcher())->DispatchX(&xev);
+
+        if (status == MessagePumpGlibXDispatcher::EVENT_QUIT) {
+          should_quit = true;
+          Quit();
+        } else if (status == MessagePumpGlibXDispatcher::EVENT_IGNORED) {
+          DLOG(WARNING) << "Event (" << xev.type << ") not handled.";
+        }
       }
 
 #if defined(HAVE_XINPUT2)
@@ -119,6 +121,18 @@ bool MessagePumpGlibX::RunOnce(GMainContext* context, bool block) {
   return retvalue;
 }
 
+bool MessagePumpGlibX::WillProcessXEvent(XEvent* xevent) {
+  ObserverListBase<Observer>::Iterator it(observers());
+  Observer* obs;
+  while ((obs = it.GetNext()) != NULL) {
+    MessagePumpXObserver* xobs =
+        static_cast<MessagePumpXObserver*>(obs);
+    if (xobs->WillProcessXEvent(xevent))
+      return true;
+  }
+  return false;
+}
+
 void MessagePumpGlibX::EventDispatcherX(GdkEvent* event, gpointer data) {
   MessagePumpGlibX* pump_x = reinterpret_cast<MessagePumpGlibX*>(data);
 
@@ -186,4 +200,8 @@ void MessagePumpGlibX::InitializeXInput2(void) {
 }
 #endif  // HAVE_XINPUT2
 
+bool MessagePumpXObserver::WillProcessXEvent(XEvent* xev) {
+  return false;
+}
+
 }  // namespace base
diff --git a/base/message_pump_glib_x.h b/base/message_pump_glib_x.h
index 60e3b5d..6bd29c9 100644
--- a/base/message_pump_glib_x.h
+++ b/base/message_pump_glib_x.h
@@ -14,6 +14,8 @@
 #include <gtk/gtk.h>
 #include <X11/X.h>
 
+typedef union _XEvent XEvent;
+
 namespace base {
 
 class MessagePumpGlibX : public MessagePumpForUI {
@@ -31,6 +33,11 @@ class MessagePumpGlibX : public MessagePumpForUI {
  private:
   static void EventDispatcherX(GdkEvent* event, gpointer data);
 
+  // Sends the event to the observers. If an observer returns true, then it does
+  // not send the event to any other observers and returns true. Returns false
+  // if no observer returns true.
+  bool WillProcessXEvent(XEvent* xevent);
+
   // Update the lookup table and flag the events that should be captured and
   // processed so that GDK doesn't get to them.
   void InitializeEventsToCapture(void);
diff --git a/base/message_pump_glib_x_dispatch.h b/base/message_pump_glib_x_dispatch.h
index 4c44cab..28f59e1 100644
--- a/base/message_pump_glib_x_dispatch.h
+++ b/base/message_pump_glib_x_dispatch.h
@@ -31,6 +31,15 @@ class MessagePumpGlibXDispatcher : public MessagePumpForUI::Dispatcher {
   virtual DispatchStatus DispatchX(XEvent* xevent) = 0;
 };
 
+class MessagePumpXObserver : public MessagePumpForUI::Observer {
+ public:
+  // This method is called before processing an XEvent. If the method returns
+  // true, it indicates the event has already been handled, so the event is not
+  // processed any farther. If the method returns false, the event dispatching
+  // proceeds as normal.
+  virtual bool WillProcessXEvent(XEvent* xevent);
+};
+
 }  // namespace base
 
 #endif  // BASE_MESSAGE_PUMP_GLIB_X_DISPATCH_H