DO NOT MERGE libgui: Remove IGBC::BufferItem

Removes IGraphicBufferConsumer::BufferItem. Depends on the
following changes:
    I187b3a7d05196b6289596afac8fb9a9d4aebff76
    I0ddd38df37500cfd6b21d1e768ed14e39c5cd9fc

Cherry-pick of Id1fa56d092188f2cb712768d5d2fc6a9027fb73c

Change-Id: I3edf0db8fba656fd78e18a5a7f1137f0fb6b237d
diff --git a/include/gui/BufferQueueCore.h b/include/gui/BufferQueueCore.h
index 797a108..40026bd 100644
--- a/include/gui/BufferQueueCore.h
+++ b/include/gui/BufferQueueCore.h
@@ -17,6 +17,7 @@
 #ifndef ANDROID_GUI_BUFFERQUEUECORE_H
 #define ANDROID_GUI_BUFFERQUEUECORE_H
 
+#include <gui/BufferItem.h>
 #include <gui/BufferQueueDefs.h>
 #include <gui/BufferSlot.h>
 
@@ -45,7 +46,6 @@
 
 namespace android {
 
-class BufferItem;
 class IConsumerListener;
 class IGraphicBufferAlloc;
 class IProducerListener;
@@ -58,7 +58,7 @@
 public:
     // Used as a placeholder slot number when the value isn't pointing to an
     // existing buffer.
-    enum { INVALID_BUFFER_SLOT = -1 }; // TODO: Extract from IGBC::BufferItem
+    enum { INVALID_BUFFER_SLOT = BufferItem::INVALID_BUFFER_SLOT };
 
     // We reserve two slots in order to guarantee that the producer and
     // consumer can run asynchronously.