Refactoring: Remove TaskRunnerHelper::Get() for ScriptState

Bug: 777775
Change-Id: Ie7dda668c7f171bf66a505495441e87db766b8b3
Reviewed-on: https://chromium-review.googlesource.com/737915
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512122}
13 files changed