This will allow to pull in gyp as a deps to the same location
as chromium (tools/gyp not build/gyp), needed for gn switch.

This is the first step of a 3-way move.
1) Copy v8.gyp in v8
2) Update references in embedders (follow up)
3) Remove old v8.gyp (follow up)

BUG=chromium:474921
LOG=n
NOTRY=true

Review URL: https://codereview.chromium.org/1920793002

Cr-Commit-Position: refs/heads/master@{#35760}