Revert "[DevTools] Allow modifying instrumenting agents while iterating."

This reverts commit a0206e7e8481b0bd171beb9fc895bd55201eff6e.
BUG=627373
R=stip@chromium.org

Review URL: https://codereview.chromium.org/2148583002 .

Cr-Commit-Position: refs/heads/master@{#404854}
3 files changed