Update V8 DEPS.
Update V8 DEPS.

Rolling v8/tools/clang to 6f504ec1a843c7c6af799768a774dec205ce4f3b

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/822073003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#25942}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh