[Extension Example] Replace sendRequest with sendMessage in timer

Fixed other JavaScript exceptions.

Test: Launch Chromium with --enable-benchmarking and timer extension
Bug: None
Change-Id: I48fba226f24fad1908254b3065a770e106d8c4a0
Reviewed-on: https://chromium-review.googlesource.com/c/1278044
Commit-Queue: Shimi Zhang <ctzsm@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599012}
4 files changed