libgui: Prepare for IGBC::BufferItem removal

Switches some dependencies from IGraphicBufferConsumer::BufferItem to
android::BufferItem and adds some methods to facilitate incrementally
changing client code to do the same.

Change-Id: I699ed0a6837076867ca756b28d1ffb2238f7a0d9
diff --git a/libs/gui/StreamSplitter.cpp b/libs/gui/StreamSplitter.cpp
index 1461337..43f9214 100644
--- a/libs/gui/StreamSplitter.cpp
+++ b/libs/gui/StreamSplitter.cpp
@@ -20,6 +20,7 @@
 #define ATRACE_TAG ATRACE_TAG_GRAPHICS
 //#define LOG_NDEBUG 0
 
+#include <gui/BufferItem.h>
 #include <gui/IGraphicBufferConsumer.h>
 #include <gui/IGraphicBufferProducer.h>
 #include <gui/StreamSplitter.h>
@@ -123,7 +124,7 @@
     ++mOutstandingBuffers;
 
     // Acquire and detach the buffer from the input
-    IGraphicBufferConsumer::BufferItem bufferItem;
+    BufferItem bufferItem;
     status_t status = mInput->acquireBuffer(&bufferItem, /* presentWhen */ 0);
     LOG_ALWAYS_FATAL_IF(status != NO_ERROR,
             "acquiring buffer from input failed (%d)", status);