If executionContextId then binding is installed only once in given
context.

R=pfeldman@chromium.org

Bug: chromium:849552
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I474fcf9ad5e704b0a12c9aaa321cc90bb7957e2c
Reviewed-on: https://chromium-review.googlesource.com/1087489
Commit-Queue: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53538}