New method I420Buffer::Copy.

webrtc/common_video/video_frame_buffer.cc

Index: webrtc/common_video/video_frame_buffer.cc
diff --git a/webrtc/common_video/video_frame_buffer.cc b/webrtc/common_video/video_frame_buffer.cc
index 19e44febaf37b9591e3790269909496b2f41225d..8720793b67da63603d033658e9967933306fb54c 100644
--- a/webrtc/common_video/video_frame_buffer.cc
+++ b/webrtc/common_video/video_frame_buffer.cc
@@ -12,6 +12,7 @@
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/keep_ref_until_done.h"
+#include "libyuv/convert.h"
 
 // Aligning pointer to 64 bytes for improved performance, e.g. use SIMD.
 static const int kBufferAlignment = 64;
@@ -117,6 +118,21 @@ rtc::scoped_refptr<VideoFrameBuffer> I420Buffer::NativeToI420Buffer() {
   return nullptr;
 }
 
+rtc::scoped_refptr<I420Buffer> I420Buffer::Copy() {
+  rtc::scoped_refptr<I420Buffer> copy =
+      new rtc::RefCountedObject<I420Buffer>(width(), height());
+  RTC_CHECK(0 == libyuv::I420Copy(
+      data(kYPlane), stride(kYPlane),
+      data(kUPlane), stride(kUPlane),
+      data(kVPlane), stride(kVPlane),
+      copy->MutableData(kYPlane), copy->stride(kYPlane),
+      copy->MutableData(kUPlane), copy->stride(kUPlane),
+      copy->MutableData(kVPlane), copy->stride(kVPlane),
+      width(), height()));
+
+  return copy;
+}
+
 NativeHandleBuffer::NativeHandleBuffer(void* native_handle,
                                        int width,
                                        int height)