Improvement on loop unrolling with loops indexing sampler arrays 1) Before this workaround is hardwired on mac, now we move it behind a compil 2) Fix the issue where "break" inside the loop isn't handled while unrolled. BUG=338474 TEST=webgl conformance test sampler-array-using-loop-index.html Change-Id: I4996a42c2dea39a8a5af772c256f8e3cb383f59a Reviewed-on: https://chromium-review.googlesource.com/188079 Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Zhenyao Mo <zmo@chromium.org> Conflicts: include/GLSLANG/ShaderLang.h src/compiler/translator/ValidateLimitations.cpp Change-Id: I546197bd7df1634ebccdd380be14c3250cd56151 Reviewed-on: https://chromium-review.googlesource.com/189061 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Zhenyao Mo <zmo@chromium.org>