GN: just new deps

These just are the DEPS changes from the previous GN CL, each rolled up to head.

I've removed the hooks to fetch GN and Clang... will have to figure out how to
deal with .gclient files in different places later.

BUG=skia:5452
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2087403002

Review-Url: https://codereview.chromium.org/2087403002
2 files changed