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/tests/StreamSplitter_test.cpp b/libs/gui/tests/StreamSplitter_test.cpp
index 429ab6c..767c7c6 100644
--- a/libs/gui/tests/StreamSplitter_test.cpp
+++ b/libs/gui/tests/StreamSplitter_test.cpp
@@ -17,6 +17,7 @@
 #define LOG_TAG "StreamSplitter_test"
 //#define LOG_NDEBUG 0
 
+#include <gui/BufferItem.h>
 #include <gui/BufferQueue.h>
 #include <gui/IConsumerListener.h>
 #include <gui/ISurfaceComposer.h>
@@ -116,7 +117,7 @@
             Fence::NO_FENCE);
     ASSERT_EQ(OK, inputProducer->queueBuffer(slot, qbInput, &qbOutput));
 
-    IGraphicBufferConsumer::BufferItem item;
+    BufferItem item;
     ASSERT_EQ(OK, outputConsumer->acquireBuffer(&item, 0));
 
     uint32_t* dataOut;
@@ -184,7 +185,7 @@
     ASSERT_EQ(OK, inputProducer->queueBuffer(slot, qbInput, &qbOutput));
 
     for (int output = 0; output < NUM_OUTPUTS; ++output) {
-        IGraphicBufferConsumer::BufferItem item;
+        BufferItem item;
         ASSERT_EQ(OK, outputConsumers[output]->acquireBuffer(&item, 0));
 
         uint32_t* dataOut;