third_party/inspector_protocol is tracked in git and ignoring it causes
problems if the tree is copied to another git repository (e.g. Node.js)
Similarly, third_party/binutils has some files checked in. This adds a
.gitignore file in this directory (same as Chromium).

R=franzih@chromium.org,ofrobots@google.com,machenbach@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2635483002
Cr-Commit-Position: refs/heads/master@{#42373}