UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36

Example URL:
http://distribution.bbb3d.renderfarming.net/video/mp4/bbb_sunflower_2160p_30fps_normal.mp4

Steps to reproduce the problem:
1. Attempt to play a h264 mp4 with resolution > 1080p (eg. 4k)
2. Note software ffmpeg is used as decoder rather than GpuVideoDecoder 

What is the expected behavior?
GpuVideoDecoder should be used for all supported formats of the GPU.

What went wrong?
This was fixed for Nvidia and Intel GPUs in this issue - https://bugs.chromium.org/p/chromium/issues/detail?id=573565

However, AMD Radeon GPUs didn't seem to get this new support.

I noted this on the original issue but figure it's worth opening a new issue just for Radeon cards.

Did this work before? No 

Is it a problem with Flash or HTML5? N/A

Does this work in other browsers? Yes 

Chrome version: 51.0.2704.103  Channel: stable
OS Version: 10.0
Flash Version: -

I've tested this on AMD Radeon GPU's (R4, R7, R9), Windows 10, Chrome 51.x and 52.x.

From testing I believe the max vertical resolution is 1088 to get GPU decoding. Anything higher will fall back to software decode.

I am able to play back these h264 mp4 videos just fine on native players (MPC-HC, Windows Movies & TV player, etc.) with GPU decoding.