Add offset support to BitstreamBuffer.

media/base/bitstream_buffer.h

Index: media/base/bitstream_buffer.h
diff --git a/media/base/bitstream_buffer.h b/media/base/bitstream_buffer.h
index fe3c8da358ab021da1255517688e3693a96b4b1e..affe430b96803826985d32b1be1a07a4db692397 100644
--- a/media/base/bitstream_buffer.h
+++ b/media/base/bitstream_buffer.h
@@ -23,19 +23,39 @@ class MEDIA_EXPORT BitstreamBuffer {
  public:
   BitstreamBuffer(int32_t id, base::SharedMemoryHandle handle, size_t size);
 
+  // Constructs a new BitstreamBuffer. The content of the bitstream is located
+  // at |offset| bytes away from the start of the shared memory and the payload
+  // is |size| bytes.
+  BitstreamBuffer(int32_t id,
+                  base::SharedMemoryHandle handle,
+                  size_t size,
+                  off_t offset);
+
   BitstreamBuffer(int32_t id,
                   base::SharedMemoryHandle handle,
                   size_t size,
                   base::TimeDelta presentation_timestamp);
 
+  BitstreamBuffer(int32_t id,
+                  base::SharedMemoryHandle handle,
+                  size_t size,
+                  off_t offset,
+                  base::TimeDelta presentation_timestamp);
+
   ~BitstreamBuffer();
 
   void SetDecryptConfig(const DecryptConfig& decrypt_config);
 
   int32_t id() const { return id_; }
   base::SharedMemoryHandle handle() const { return handle_; }
+
+  // The number of bytes of the actual bitstream data. It is the size of the
+  // content instead of the whole shared memory.
   size_t size() const { return size_; }
 
+  // The offset to the start of actual bitstream data in the shared memory.
+  off_t offset() const { return offset_; }
+
   // The timestamp is only valid if it's not equal to |media::kNoTimestamp()|.
   base::TimeDelta presentation_timestamp() const {
     return presentation_timestamp_;
@@ -51,6 +71,7 @@ class MEDIA_EXPORT BitstreamBuffer {
   int32_t id_;
   base::SharedMemoryHandle handle_;
   size_t size_;
+  off_t offset_;
 
   // This is only set when necessary. For example, AndroidVideoDecodeAccelerator
   // needs the timestamp because the underlying decoder may require it to