Step 1 of opts_crc32 rollout.

  - This adds an crc32_sources variable to opts.gypi and hooks it into
    our GYP build with a dummy source file.

Step 2 will hook crc32_sources into Chrome's GN build.
Step 3 will actually land some code using CRC32 instructions.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259233002

Review-Url: https://codereview.chromium.org/2259233002
2 files changed