content_shell: add --run-web-tests to replace --run-layout-test.

Rename switches::IsRunLayoutTestSwitchPresent to
IsRunWebTestsSwitchPresent.

Note that we decided to rename LayoutTests to web_tests.
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/KKNbuzj-3HY/H8FWgtKrBgAJ

NOPRESUBMIT due to crbug.com/841656.

NOPRESUBMIT=true

Bug: 843412
Change-Id: I03db1e3a427265b926d8d0811b4cea7d34cd8a70
Reviewed-on: https://chromium-review.googlesource.com/1053328
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558998}
27 files changed