Fix downloading of LLVM Gold plugin for the official Chrome.

The build needs the plugin to make an LTO build, which will soon
be the default for the official Chrome as a part of
Control Flow Integrity launch. See
https://sites.google.com/a/chromium.org/dev/developers/testing/control-flow-integrity
for more details.

BUG=chromium:464797

Review URL: https://codereview.chromium.org/1475173002

Cr-Commit-Position: refs/heads/master@{#361774}
1 file changed