Add offset support to BitstreamBuffer.

content/common/gpu/media/android_video_decode_accelerator.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/gpu/media/android_video_decode_accelerator.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
@@ skipping 188 matching lines @@
   TRACE_COUNTER1("media", "AVDA::PendingBitstreamBufferCount",
                  pending_bitstream_buffers_.size());
 
   if (bitstream_buffer.id() == -1) {
     media_codec_->QueueEOS(input_buf_index);
     return;
   }
 
   scoped_ptr<base::SharedMemory> shm(
       new base::SharedMemory(bitstream_buffer.handle(), true));
-  RETURN_ON_FAILURE(this, shm->Map(bitstream_buffer.size()),
-                    "Failed to SharedMemory::Map()", UNREADABLE_INPUT);
+  RETURN_ON_FAILURE(
+      this, shm->MapAt(bitstream_buffer.offset(), bitstream_buffer.size()),

[Pawel Osciak, 2015/12/24 00:58:01]

MapAt (and underlying mmap()) requires offset to be aligned to PAGE_SIZE (or
base::SysInfo::VMAllocationGranularity()). Are we able to guarantee that?
But perhaps it would be simpler to map as usual, without offset, and just use
pointer+offset below?

[Owen Lin, 2015/12/24 08:01:35]

I think we can do it in ArcCodec. Align the input buffer size to PAGE_SIZE. 

+      "Failed to SharedMemory::Map()", UNREADABLE_INPUT);
 
   const base::TimeDelta presentation_timestamp =
       bitstream_buffer.presentation_timestamp();
   DCHECK(presentation_timestamp != media::kNoTimestamp())
       << "Bitstream buffers must have valid presentation timestamps";
 
   // There may already be a bitstream buffer with this timestamp, e.g., VP9 alt
   // ref frames, but it's OK to overwrite it because we only expect a single
   // output frame to have that timestamp. AVDA clients only use the bitstream
   // buffer id in the returned Pictures to map a bitstream buffer back to a
@@ skipping 445 matching lines @@
     // software fallback for H264 on Android anyway.
     profile.max_resolution.SetSize(3840, 2160);
     profiles.push_back(profile);
   }
 #endif
 
   return profiles;
 }
 
 }  // namespace content