This enables downloading all gcmole dependencies from
google storage on demand, controlled by a gyp flag
"gcmole=1". This makes the analysis portable to any linux64
host. The archive contains a prebuilt clang in the needed
version, the gcmole plugin and a lua binary.

The tool can be run through a new wrapper that sets up the
environment. This'll ease running it on swarming.

BUG=chromium:535160
LOG=n

Review URL: https://codereview.chromium.org/1703533002

Cr-Commit-Position: refs/heads/master@{#34046}