GitLab

Add sendBrowserTestCommand that expects a 'string' result: this helper
retries until a 'string' result is received, and logs errors.

Update sendTestMessage docs (change message -> command) and update the
test extension harness to use sendBrowserTestCommand.

Bug: 891148
Change-Id: I5840668919672e68787eccd8dece3eae5f2d8c45
Reviewed-on: https://chromium-review.googlesource.com/1256482Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595733}