Mojo: Add a "GetType()" to Dispatchers.

mojo/system/dispatcher.h

Index: mojo/system/dispatcher.h
diff --git a/mojo/system/dispatcher.h b/mojo/system/dispatcher.h
index b405d1aad402235440abd5421d201755b925caa8..ca7aa4f2a4dff7eb822443279dd3dbc2482b853d 100644
--- a/mojo/system/dispatcher.h
+++ b/mojo/system/dispatcher.h
@@ -27,6 +27,14 @@ class Waiter;
 class MOJO_SYSTEM_IMPL_EXPORT Dispatcher :
     public base::RefCountedThreadSafe<Dispatcher> {
  public:
+  enum Type {
+    kTypeUnknown = 0,
+    kTypeMessagePipe,
+    kTypeDataPipeProducer,
+    kTypeDataPipeConsumer
+  };
+  virtual Type GetType() = 0;
+
   // These methods implement the various primitives named |Mojo...()|. These
   // take |lock_| and handle races with |Close()|. Then they call out to
   // subclasses' |...ImplNoLock()| methods (still under |lock_|), which actually