Add BufferItemConsumer, a simple BufferQueue consumer.

BufferItemConsumer allows for acquiring BufferQueue's BufferItems,
which contain all the data and metadata the BufferQueue has for a
given graphics buffer.

This consumer is useful when direct access to the native buffer_handles
is needed by the client.

Also includes a minor cleanup of CpuConsumer's use of 'virtual'.

Bug: 6243944
Change-Id: If7dc4192b15ac499555f1eda42a85140f2434795
diff --git a/libs/gui/Android.mk b/libs/gui/Android.mk
index 3aa3a50..2bf363f 100644
--- a/libs/gui/Android.mk
+++ b/libs/gui/Android.mk
@@ -23,7 +23,8 @@
 	Surface.cpp \
 	SurfaceComposerClient.cpp \
 	DummyConsumer.cpp \
-	CpuConsumer.cpp
+	CpuConsumer.cpp \
+	BufferItemConsumer.cpp
 
 LOCAL_SHARED_LIBRARIES := \
 	libbinder \