libvpx: Pull from upstream

source/libvpx/vp9/common/vp9_scale.h

Index: source/libvpx/vp9/common/vp9_scale.h
===================================================================
--- source/libvpx/vp9/common/vp9_scale.h	(revision 281795)
+++ source/libvpx/vp9/common/vp9_scale.h	(working copy)
@@ -46,10 +46,18 @@
 }
 
 static INLINE int vp9_is_scaled(const struct scale_factors *sf) {
-  return sf->x_scale_fp != REF_NO_SCALE ||
-         sf->y_scale_fp != REF_NO_SCALE;
+  return vp9_is_valid_scale(sf) &&
+         (sf->x_scale_fp != REF_NO_SCALE || sf->y_scale_fp != REF_NO_SCALE);
 }
 
+static INLINE int valid_ref_frame_size(int ref_width, int ref_height,
+                                      int this_width, int this_height) {
+  return 2 * this_width >= ref_width &&
+         2 * this_height >= ref_height &&
+         this_width <= 16 * ref_width &&
+         this_height <= 16 * ref_height;
+}
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif