libgui: Remove RefBase from BitTube

Removes RefBase from BitTube, since because it is not a Binder object,
it doesn't need to be reference-counted in this way.

In the process, we rename IDisplayEventConnection::getDataChannel to
IDEC::stealReceiveChannel to make it clearer that this is a non-const
operation on the remote end that removes its access to the receive
channel.

This also adds a couple of methods for moving the receive file
descriptor out of one BitTube and into another, since this is the
essence of the IDisplayEventConnection::stealReceiveChannel method,
and now with C++11 move semantics, we can do this without needing to
return an sp<> from EventThread's implementation of stealReceiveChannel.

Test: m -j + manual testing
Change-Id: Ibaaca2a14fb6155052fe5434c14bc3e671b43743
diff --git a/services/surfaceflinger/EventThread.h b/services/surfaceflinger/EventThread.h
index 3e05749..6a59fbb 100644
--- a/services/surfaceflinger/EventThread.h
+++ b/services/surfaceflinger/EventThread.h
@@ -20,6 +20,7 @@
 #include <stdint.h>
 #include <sys/types.h>
 
+#include <private/gui/BitTube.h>
 #include <gui/DisplayEventReceiver.h>
 #include <gui/IDisplayEventConnection.h>
 
@@ -68,11 +69,11 @@
     private:
         virtual ~Connection();
         virtual void onFirstRef();
-        status_t getDataChannel(sp<gui::BitTube>* outChannel) const override;
+        status_t stealReceiveChannel(gui::BitTube* outChannel) override;
         status_t setVsyncRate(uint32_t count) override;
         void requestNextVsync() override;    // asynchronous
         sp<EventThread> const mEventThread;
-        sp<gui::BitTube> const mChannel;
+        gui::BitTube mChannel;
     };
 
 public: