GitLab

We can expose test_runner::WebTask as blink::WebTaskRunner::Task.
Doing this means that components/test_runner/web_task.h header
no longer needs to be included outside of components/test_runner.

BUG=595089

Review URL: https://codereview.chromium.org/1805753002

Cr-Commit-Position: refs/heads/master@{#381826}