libgui: Add BufferItem(IGBC::BufferItem)

Add a constructor for building a BufferItem from an
IGraphicBufferConsumer::BufferItem.

Change-Id: I1394e693314429ada93427889f10b7b01c948053
diff --git a/include/gui/BufferItem.h b/include/gui/BufferItem.h
index fecdbc1..112c482 100644
--- a/include/gui/BufferItem.h
+++ b/include/gui/BufferItem.h
@@ -44,6 +44,7 @@
     // The default value of mBuf, used to indicate this doesn't correspond to a slot.
     enum { INVALID_BUFFER_SLOT = -1 };
     BufferItem();
+    BufferItem(const IGraphicBufferConsumer::BufferItem& item);
     ~BufferItem();
     operator IGraphicBufferConsumer::BufferItem() const;