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Adjust alt-ref selection in define_gf_group()

107de19698 changes the encoder alt-ref selection behavior. Assuming
min_gf_interval = max_gf_interval = 4, the frame order would be
frm_1  arf_1  frm_2  frm_3  frm_4  frm_5  arf_2 before 107de19698;
frm_1  arf_1  frm_2  frm_3  frm_4  arf_2  frm_5 after 107de19698.

This patch reverts such alt-ref placement change.

Change-Id: I93a4a65036575151286f004d455d4fcea88a1550

--- a/vp9/encoder/vp9_firstpass.c

+++ b/vp9/encoder/vp9_firstpass.c

@@ -2370,8 +2370,8 @@

                                                 cpi->common.bit_depth));

     active_min_gf_interval =

         rc->min_gf_interval + arf_active_or_kf + VPXMIN(2, int_max_q / 200);

-    if (active_min_gf_interval > rc->max_gf_interval)

-      active_min_gf_interval = rc->max_gf_interval;

+    active_min_gf_interval =

+        VPXMIN(active_min_gf_interval, rc->max_gf_interval + arf_active_or_kf);

     if (cpi->multi_arf_allowed) {

       active_max_gf_interval = rc->max_gf_interval;

@@ -2382,11 +2382,14 @@

       // interval to spread the cost of the GF.

       active_max_gf_interval = 12 + arf_active_or_kf + VPXMIN(4, (int_lbq / 6));

-      // We have: active_min_gf_interval <= rc->max_gf_interval

-      if (active_max_gf_interval < active_min_gf_interval)

+      // We have: active_min_gf_interval <=

+      // rc->max_gf_interval + arf_active_or_kf.

+      if (active_max_gf_interval < active_min_gf_interval) {

         active_max_gf_interval = active_min_gf_interval;

-      else if (active_max_gf_interval > rc->max_gf_interval)

-        active_max_gf_interval = rc->max_gf_interval;

+      } else {

+        active_max_gf_interval = VPXMIN(active_max_gf_interval,

+                                        rc->max_gf_interval + arf_active_or_kf);

+      }

       // Would the active max drop us out just before the near the next kf?

       if ((active_max_gf_interval <= rc->frames_to_key) &&