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..6f49e8aef9d0f1f387ff15cce119aca0699567ac 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 +118,23 @@ rtc::scoped_refptr<VideoFrameBuffer> I420Buffer::NativeToI420Buffer() {
   return nullptr;
 }
 
+rtc::scoped_refptr<I420Buffer> I420Buffer::Copy(
+    const rtc::scoped_refptr<VideoFrameBuffer>& buffer) {
+  int width = buffer->width();
+  int height = buffer->height();
+  rtc::scoped_refptr<I420Buffer> copy =
+      new rtc::RefCountedObject<I420Buffer>(width, height);
+  RTC_CHECK(libyuv::I420Copy(buffer->data(kYPlane), buffer->stride(kYPlane),
+                             buffer->data(kUPlane), buffer->stride(kUPlane),
+                             buffer->data(kVPlane), buffer->stride(kVPlane),
+                             copy->MutableData(kYPlane), copy->stride(kYPlane),
+                             copy->MutableData(kUPlane), copy->stride(kUPlane),
+                             copy->MutableData(kVPlane), copy->stride(kVPlane),
+                             width, height) == 0);
+
+  return copy;
+}
+
 NativeHandleBuffer::NativeHandleBuffer(void* native_handle,
                                        int width,
                                        int height)