Reland of Add experimental simulcast screen content mode

webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.cc

Index: webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.cc
diff --git a/webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.cc b/webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.cc
index 7807d45d7aaf70403343d692e9cad9773bde1ede..f842fb4213379e95980417a5a13b3e015407dcb4 100644
--- a/webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/realtime_temporal_layers.cc
@@ -94,11 +94,11 @@ class RealTimeTemporalLayers : public TemporalLayers {
         timestamp_(0),
         last_base_layer_sync_(0),
         layer_ids_length_(0),
-        layer_ids_(NULL),
+        layer_ids_(nullptr),
         encode_flags_length_(0),
-        encode_flags_(NULL) {
+        encode_flags_(nullptr) {
     RTC_CHECK_GE(max_temporal_layers_, 1);
-    RTC_CHECK_GE(max_temporal_layers_, 3);
+    RTC_CHECK_LE(max_temporal_layers_, 3);
   }
 
   virtual ~RealTimeTemporalLayers() {}