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This CL contains a basic fuzzer for WebGL shaders that shows some
essential design ideas:

1) a protobuf spec defines how shaders will be generated
2) conversion from protobuf message to shader string is
   provided in its own library that has unit tests
3) we add a basic fuzzer to compile shader programs using libANGLE

This is by no means complete and serves as a foundation for the fuzzer
so subsequent CLs will be easier to review. Later CLs will slowly complete
the core grammar for GLSL before incorporating some more complex testcases
from the Khronos compliance suite.

BUG=900487

Change-Id: I67df52a73926d22637afad9a966790f34011175c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1623556
Commit-Queue: Ned Williamson <nedwill@google.com>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662832}