fix a bug when reallocating a window's buffers is needed

we need to mark the buffers that need to be reallocated,
NOT the buffer's indices.

Change-Id: I809e2e1b03b56c4d2ab983c25523dae99aa1da74
diff --git a/include/private/surfaceflinger/SharedBufferStack.h b/include/private/surfaceflinger/SharedBufferStack.h
index c3ac317..de54870 100644
--- a/include/private/surfaceflinger/SharedBufferStack.h
+++ b/include/private/surfaceflinger/SharedBufferStack.h
@@ -303,6 +303,7 @@
             : mCapacity(c), mList(0) { }
         status_t add(int value);
         status_t remove(int value);
+        uint32_t getMask() const { return mList; }
 
         class const_iterator {
             friend class BufferList;