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 217be7610e4684dd259918d90f20217879c3d26d..10ce2b632c76de0ba8627423421b9f0dc95b4ad7 100644
--- a/media/base/bitstream_buffer.h
+++ b/media/base/bitstream_buffer.h
@@ -24,12 +24,17 @@ class MEDIA_EXPORT BitstreamBuffer {
  public:
   BitstreamBuffer();
 
-  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. When not provided, the default value for |offset| is 0.
+  // |presentation_timestamp| is when the decoded frame should be displayed.
+  // When not provided, |presentation_timestamp| will be
+  // |media::kNoTimestamp()|.
   BitstreamBuffer(int32_t id,
                   base::SharedMemoryHandle handle,
                   size_t size,
-                  base::TimeDelta presentation_timestamp);
+                  off_t offset = 0,
+                  base::TimeDelta presentation_timestamp = kNoTimestamp());
 
   ~BitstreamBuffer();
 
@@ -37,15 +42,21 @@ class MEDIA_EXPORT BitstreamBuffer {
 
   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_; }
 
-  void set_handle(const base::SharedMemoryHandle& handle) { handle_ = handle; }
+  // 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_;
   }
 
+  void set_handle(const base::SharedMemoryHandle& handle) { handle_ = handle; }
+
   // The following methods come from DecryptConfig.
 
   const std::string& key_id() const { return key_id_; }
@@ -56,6 +67,7 @@ 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