libvpx: Pull from upstream

source/libvpx/vp8/encoder/ethreading.c

Index: source/libvpx/vp8/encoder/ethreading.c
===================================================================
--- source/libvpx/vp8/encoder/ethreading.c	(revision 290053)
+++ source/libvpx/vp8/encoder/ethreading.c	(working copy)
@@ -206,6 +206,21 @@
                         }
 
 #endif
+                        // Keep track of how many (consecutive) times a  block
+                        // is coded as ZEROMV_LASTREF, for base layer frames.
+                        // Reset to 0 if its coded as anything else.
+                        if (cpi->current_layer == 0) {
+                          if (xd->mode_info_context->mbmi.mode == ZEROMV &&
+                              xd->mode_info_context->mbmi.ref_frame ==
+                                  LAST_FRAME) {
+                            // Increment, check for wrap-around.
+                            if (cpi->consec_zero_last[map_index+mb_col] < 255)
+                              cpi->consec_zero_last[map_index+mb_col] +=
+                                  1;
+                          } else {
+                            cpi->consec_zero_last[map_index+mb_col] = 0;
+                          }
+                        }
 
                         /* Special case code for cyclic refresh
                          * If cyclic update enabled then copy