Add offset support to BitstreamBuffer.

content/common/gpu/media/android_video_decode_accelerator.cc

Index: content/common/gpu/media/android_video_decode_accelerator.cc
diff --git a/content/common/gpu/media/android_video_decode_accelerator.cc b/content/common/gpu/media/android_video_decode_accelerator.cc
index 00e1bb67856e14163ea5da84a6d04a37607335de..62efb68dfe5f04ff96c4282730c2c2aa17384b89 100644
--- a/content/common/gpu/media/android_video_decode_accelerator.cc
+++ b/content/common/gpu/media/android_video_decode_accelerator.cc
@@ -206,8 +206,9 @@ void AndroidVideoDecodeAccelerator::QueueInput() {
 
   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();