SF: Force refresh when in single buffer mode

- Add a boolean to BufferItem to track whether single buffer mode is
  enabled. When it is, force SurfaceFlinger to acquire a new buffer
  and refresh on every vsync.

Bug 24940410

Change-Id: Iea67330c416b6fb14500865f98c67f1c12f23197
diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index 268c9da..ef01745 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -744,6 +744,8 @@
                 mCore->mDequeueBufferCannotBlock ||
                 (mCore->mSingleBufferMode && mCore->mSingleBufferSlot == slot);
         item.mSurfaceDamage = surfaceDamage;
+        item.mSingleBufferMode = mCore->mSingleBufferMode;
+        item.mQueuedBuffer = true;
 
         mStickyTransform = stickyTransform;