media: VideoFrame: add offset for shared memory buffers

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index 4215bae1786086854b52c44302245e4d01d6de5a..fc4a09d81fcc2b91c0aa06e71ab7db1a0f0991f9 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -139,6 +139,7 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
       uint8* data,
       size_t data_size,
       base::SharedMemoryHandle handle,
+      size_t shared_memory_offset,
       base::TimeDelta timestamp,
       const base::Closure& no_longer_needed_cb);
 
@@ -300,6 +301,9 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // Returns the shared-memory handle, if present
   base::SharedMemoryHandle shared_memory_handle() const;
 
+  // Returns the offset into the shared memory where the frame data begins.
+  size_t shared_memory_offset() const;
+
   bool allow_overlay() const { return allow_overlay_; }
 
 #if defined(OS_POSIX)
@@ -393,6 +397,9 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // Shared memory handle, if this frame was allocated from shared memory.
   base::SharedMemoryHandle shared_memory_handle_;
 
+  // Offset in shared memory buffer.
+  size_t shared_memory_offset_;
+
 #if defined(OS_POSIX)
   // Dmabufs for each plane, if this frame is wrapping memory
   // acquired via dmabuf.