This avoids introducing an include path outside v8. Instead, the path
to where tracing includes are located is provided via a variable.

Please refer to https://codereview.chromium.org/2068073002.

Once the v8 change makes its way to chromium, we can remove the
TODO in this current change.

BUG=

Review-Url: https://codereview.chromium.org/2061933002
Cr-Commit-Position: refs/heads/master@{#37049}