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 605ff78af2a3703b271c480ca6d07649fbcd50f6..6f6d92e5acf9f96e7b8ca2e5559a17f7229c5032 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -138,6 +138,7 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
       uint8* data,
       size_t data_size,
       base::SharedMemoryHandle handle,
+      size_t data_offset,

[bbudge, 2015/01/28 18:47:07]

Naming this 'data_offset' makes it look odd that it isn't grouped with data and
data_size.
How about naming this to match shared_memory_offset below?

[llandwerlin-old, 2015/01/30 08:03:41]

Done.

       base::TimeDelta timestamp,
       const base::Closure& no_longer_needed_cb);
 
@@ -299,6 +300,9 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // Returns the shared-memory handle, if present
   base::SharedMemoryHandle shared_memory_handle() const;
 
+  // Return the offset with the shared-memory handle.

[bbudge, 2015/01/28 18:47:07]

Nit: wording. How about..
// Return the offset into the shared memory where the frame data begins.

[llandwerlin-old, 2015/01/30 08:03:40]

Done.

+  size_t shared_memory_offset() const;
+
 #if defined(OS_POSIX)
   // Returns backing dmabuf file descriptor for given |plane|, if present.
   int dmabuf_fd(size_t plane) const;
@@ -390,6 +394,9 @@ 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.