Update V8 DEPS.

Rolling v8/tools/clang to 51f59463cfea7fc19d085253cf9bd40c1b4c0038

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/830473002

Cr-Commit-Position: refs/heads/master@{#25943}
Update V8 DEPS.

Rolling v8/tools/clang to c945be21f6485fa177b43814f910b76cce921653

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/829733002

Cr-Commit-Position: refs/heads/master@{#25944}