Set lag_in_frames to 0, end usage to CBR in rt

Set g_lag_in_frames to 0 and rc_end_usage to AOM_CBR in the encoder
config defaults for AOM_USAGE_REAL_TIME.

These are the values used in WebRTC.

BUG=aomedia:2966

Change-Id: I940f94c822387b42f9dcf3632a740953fece7583
diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index f830926..4066fc3 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -3384,7 +3384,7 @@
 
       AOM_RC_ONE_PASS,  // g_pass
 
-      1,  // g_lag_in_frames
+      0,  // g_lag_in_frames
 
       0,                // rc_dropframe_thresh
       RESIZE_NONE,      // rc_resize_mode
diff --git a/test/encode_test_driver.cc b/test/encode_test_driver.cc
index c95a86d..d8a19be 100644
--- a/test/encode_test_driver.cc
+++ b/test/encode_test_driver.cc
@@ -93,8 +93,9 @@
     case kOnePassGood:
     case kTwoPassGood: break;
     case kRealTime: {
-      cfg_.g_lag_in_frames = 0;
       cfg_.g_usage = AOM_USAGE_REALTIME;
+      cfg_.g_lag_in_frames = 0;
+      cfg_.rc_end_usage = AOM_CBR;
       break;
     }
     default: ASSERT_TRUE(false) << "Unexpected mode " << mode;
diff --git a/test/rt_end_to_end_test.cc b/test/rt_end_to_end_test.cc
index fade1e8..58b68e2 100644
--- a/test/rt_end_to_end_test.cc
+++ b/test/rt_end_to_end_test.cc
@@ -89,7 +89,6 @@
     InitializeConfig();
     SetMode(::libaom_test::kRealTime);
 
-    cfg_.rc_end_usage = AOM_CBR;
     cfg_.g_threads = threads_;
     cfg_.rc_buf_sz = 1000;
     cfg_.rc_buf_initial_sz = 500;