New static I420Buffer::Rotate method, to replace GetCopyWithRotationApplied.

webrtc/common_video/include/video_frame_buffer.h

Index: webrtc/common_video/include/video_frame_buffer.h
diff --git a/webrtc/common_video/include/video_frame_buffer.h b/webrtc/common_video/include/video_frame_buffer.h
index 94b3d5d8330ed320c6703bcdb890dfa40b87539c..674397020369a92b55bac8668c04a645d1c2e68c 100644
--- a/webrtc/common_video/include/video_frame_buffer.h
+++ b/webrtc/common_video/include/video_frame_buffer.h
@@ -18,6 +18,7 @@
 #include "webrtc/base/callback.h"
 #include "webrtc/base/refcount.h"
 #include "webrtc/base/scoped_ref_ptr.h"
+#include "webrtc/common_video/rotation.h"
 #include "webrtc/system_wrappers/include/aligned_malloc.h"
 
 namespace webrtc {
@@ -130,6 +131,13 @@ class I420Buffer : public VideoFrameBuffer {
   static rtc::scoped_refptr<I420Buffer> CopyKeepStride(
       const rtc::scoped_refptr<VideoFrameBuffer>& buffer);
 
+  // Returns a rotated versions of |src|. Native buffers are not
+  // supported. The reason this function doesn't return an I420Buffer,
+  // is that it returns |src| unchanged in case |rotation| is zero.
+  static rtc::scoped_refptr<VideoFrameBuffer> Rotate(
+      const rtc::scoped_refptr<VideoFrameBuffer>& src,
+      VideoRotation rotation);
+
  protected:
   ~I420Buffer() override;