Reland of Add ability to scale to arbitrary factors

webrtc/media/base/adaptedvideotracksource.cc

Index: webrtc/media/base/adaptedvideotracksource.cc
diff --git a/webrtc/media/base/adaptedvideotracksource.cc b/webrtc/media/base/adaptedvideotracksource.cc
index acc147cc8903c6da2a7578fbcb8bb23a5c074659..5900439e12103da6b32926b2e816fa076062b80e 100644
--- a/webrtc/media/base/adaptedvideotracksource.cc
+++ b/webrtc/media/base/adaptedvideotracksource.cc
@@ -16,6 +16,11 @@ AdaptedVideoTrackSource::AdaptedVideoTrackSource() {
   thread_checker_.DetachFromThread();
 }
 
+AdaptedVideoTrackSource::AdaptedVideoTrackSource(int required_alignment)
+    : video_adapter_(required_alignment) {
+  thread_checker_.DetachFromThread();
+}
+
 bool AdaptedVideoTrackSource::GetStats(Stats* stats) {
   rtc::CritScope lock(&stats_crit_);