Workaround interpolation qualifier mismatching Centroid implies smooth when doing translation. But the Intel Mesa driver considers centroid and smooth are different interpolation qualifiers which makes shaders fail compilation. This patch adds smooth at the front of centroid at translation step. And it makes linkage.varying.rules.differing_interpolation_2 test in WebGL 2.0 dEQP test pass. BUG=621031 TEST=WebGL 2.0 deqp/data/gles3/shaders/linkage.html Change-Id: I8f0944846b5244b21c526ae95a7ce37c1504efb7 Reviewed-on: https://chromium-review.googlesource.com/360638 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Zhenyao Mo <zmo@chromium.org>