Split src/opts source lists out of opts.gyp.

This should make it easier to keep our opts.gyp in sync with Chrome's GYP and GN.

BUG=skia:

Landing this without review as a mega-tryjob.
TBR=reed@google.com

Committed: https://skia.googlesource.com/skia/+/c98fe3aa4f8c97c462c0eb6d9106fc37e48d7f82

Review URL: https://codereview.chromium.org/870353003
3 files changed