libvpx: Pull from upstream

source/libvpx/vp9/common/vp9_mvref_common.c

Index: source/libvpx/vp9/common/vp9_mvref_common.c
diff --git a/source/libvpx/vp9/common/vp9_mvref_common.c b/source/libvpx/vp9/common/vp9_mvref_common.c
index 51aa82411a9254d89b49574b7208e482f5ba0a28..52a731329d3ec8de5f8a9ea4d17e9bd205daec7f 100644
--- a/source/libvpx/vp9/common/vp9_mvref_common.c
+++ b/source/libvpx/vp9/common/vp9_mvref_common.c
@@ -69,13 +69,23 @@ static void find_mv_refs_idx(const VP9_COMMON *cm, const MACROBLOCKD *xd,
     }
   }
 
-  // Synchronize here for frame parallel decode if sync function is provided.
-  if (sync != NULL) {
-    sync(data, mi_row);
-  }
+  // TODO(hkuang): Remove this sync after fixing pthread_cond_broadcast
+  // on windows platform. The sync here is unncessary if use_perv_frame_mvs
+  // is 0. But after removing it, there will be hang in the unit test on windows
+  // due to several threads waiting for a thread's signal.
+#if defined(_WIN32) && !HAVE_PTHREAD_H
+    if (cm->frame_parallel_decode && sync != NULL) {
+      sync(data, mi_row);
+    }
+#endif
 
   // Check the last frame's mode and mv info.
   if (cm->use_prev_frame_mvs) {
+    // Synchronize here for frame parallel decode if sync function is provided.
+    if (cm->frame_parallel_decode && sync != NULL) {
+      sync(data, mi_row);
+    }
+
     if (prev_frame_mvs->ref_frame[0] == ref_frame) {
       ADD_MV_REF_LIST(prev_frame_mvs->mv[0], refmv_count, mv_ref_list, Done);
     } else if (prev_frame_mvs->ref_frame[1] == ref_frame) {