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Adds GYP and GN build files. Only building C++ code. Architecture-specific assembly code will be added in follow-up CL(s).

(This is a reupload of https://codereview.chromium.org/1403893007/ after having split it up into pieces and removed decoding and tests).

BUG=500605, 468365

Review URL: https://codereview.chromium.org/1446453004

Cr-Commit-Position: refs/heads/master@{#363443}