Consolidate message observer API for win and aura (and touch).

base/message_pump_observer.h

+// Copyright (c) 2011 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 BASE_MESSAGE_PUMP_OBSERVER_H
+#define BASE_MESSAGE_PUMP_OBSERVER_H
+
+#if defined(USE_X11)
+typedef union _XEvent XEvent;
+#endif
+
+namespace base {
+
+#if defined(OS_WIN)
+typedef MSG NativeEvent;
+#elif defined(USE_X11)
+typedef XEvent* NativeEvent;
+#endif
+
+enum EventStatus {
+  EVENT_CONTINUE,    // The event should be dispatched as normal.
+#if defined(USE_X11)
+  EVENT_HANDLED      // The event should not be processed any farther.
+#endif
+};
+
+// A MessagePumpObserver is an object that receives global
+// notifications from the UI MessageLoop with MessagePumpWin or
+// MessagePumpX.
+//
+// NOTE: An Observer implementation should be extremely fast!
+//
+// For use with MessagePumpX, please see message_pump_glib.h for more
+// info about how this is invoked in this environment.
+class BASE_EXPORT MessagePumpObserver {
+ public:
+  // This method is called before processing a NativeEvent. If the
+  // method returns EVENT_HANDLED, it indicates the event has already
+  // been handled, so the event is not processed any farther. If the
+  // method returns EVENT_CONTINUE, the event dispatching proceeds as
+  // normal.
+  virtual EventStatus WillProcessEvent(const NativeEvent& event) = 0;
+
+  // This method is called after processing a message. This method
+  // will not be called if WillProcessEvent returns EVENT_HANDLED.
+  virtual void DidProcessEvent(const NativeEvent& event) = 0;
+
+ protected:
+  virtual ~MessagePumpObserver() {}
+};
+
+}  // namespace base
+
+#endif  // BASE_MESSAGE_PUMP_OBSERVER_VIEWS_H