Adjust variance threshold for 16x16 split at low resolutions.

Change-Id: I635e37f81237e9703d7d9a11ed76a043f4ec6eb0

test/resize_test.cc

@@ -407,7 +407,7 @@ TEST_P(ResizeRealtimeTest, TestInternalResizeDownUpChangeBitRate) {
   // Disable dropped frames.
   cfg_.rc_dropframe_thresh = 0;
   // Starting bitrate low.
-  cfg_.rc_target_bitrate = 100;
+  cfg_.rc_target_bitrate = 90;
   ASSERT_NO_FATAL_FAILURE(RunLoop(&video));
 
   unsigned int last_w = cfg_.g_w;

vp9/encoder/vp9_encodeframe.c

@@ -500,7 +500,7 @@ static void set_vbp_thresholds(VP9_COMP *cpi, int64_t thresholds[], int q) {
     if (cm->width <= 352 && cm->height <= 288) {
       thresholds[0] = threshold_base >> 3;
       thresholds[1] = threshold_base >> 1;
-      thresholds[2] = threshold_base << 2;
+      thresholds[2] = threshold_base << 3;
     } else {
       thresholds[0] = threshold_base;
       thresholds[1] = (5 * threshold_base) >> 2;