Chrome Version: 56.0.2902.0
Chrome OS Version:8938.0.2016_10-27_2240
Chrome OS Platform: Acer Chromebook R11

Please specify Cr-* of the system to which this bug/feature applies (add
the label below).

Steps To Reproduce:
(1) Enable WebGL 2.0 Prototype for chrome, open the link "chrome://flags", enable "WebGL 2.0 Prototype", and click "RELAUNCH NOW".
(2) Open the link https://www.khronos.org/registry/webgl/sdk/tests/conformance2/reading/read-pixels-from-fbo-test.html?webglVersion=2&quiet=0, and will run the case automatically.

Expected Result:
This case passes on Mesa driver. 

Actual Result:
This case fails. 

Reproducibility: Always

This case passes on Linux + mesa platform with Mesa TOT, and the issue was fixed by https://bugs.freedesktop.org/show_bug.cgi?id=94345
The fix need to apply to ChromiumOS.