Add ability to scale to arbitrary factors

webrtc/media/base/adaptedvideotracksource.h

Index: webrtc/media/base/adaptedvideotracksource.h
diff --git a/webrtc/media/base/adaptedvideotracksource.h b/webrtc/media/base/adaptedvideotracksource.h
index 5b420aeb9e1d344bc9e20667b85a12eaea7052b4..9d51c692c2a7941f935e73e9caf6686f80ce2744 100644
--- a/webrtc/media/base/adaptedvideotracksource.h
+++ b/webrtc/media/base/adaptedvideotracksource.h
@@ -28,6 +28,9 @@ class AdaptedVideoTrackSource
   AdaptedVideoTrackSource();
 
  protected:
+  // Allows derived classes to initialize |video_adapter_| with a custom
+  // alignment.
+  AdaptedVideoTrackSource(int required_alignment);
   // Checks the apply_rotation() flag. If the frame needs rotation, and it is a
   // plain memory frame, it is rotated. Subclasses producing native frames must
   // handle apply_rotation() themselves.