Temporarily re-introduce load-component-extension switch.

BUG=chromedriver:1625,615096

Review-Url: https://codereview.chromium.org/2680883003
Cr-Commit-Position: refs/heads/master@{#450581}
(cherry picked from commit 5da9a9aed98a274658b923478a68968f348ec5b5)

Review-Url: https://codereview.chromium.org/2702203005 .
Cr-Commit-Position: refs/branch-heads/2987@{#628}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
1 file changed