libvpx: Pull from upstream

source/libvpx/vp8/encoder/encodeframe.c

Index: source/libvpx/vp8/encoder/encodeframe.c
===================================================================
--- source/libvpx/vp8/encoder/encodeframe.c	(revision 290053)
+++ source/libvpx/vp8/encoder/encodeframe.c	(working copy)
@@ -522,6 +522,19 @@
             }
 
 #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 xd->mbmi.segment_id; (which