[DOMWebSocket] Validate subprotocols before creating a channel instance

We don't have to create a channel instance to validate subprotocols.

BUG=none

Review URL: https://codereview.chromium.org/612783002

git-svn-id: svn://svn.chromium.org/blink/trunk@182896 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Transfer SecurityOrigin overrides to Workers.

Should a Document be operating with a SecurityOrigin that grants
(powerful) abilities like disabling same-origin policy or allows
file access, have those transfer over to any new Workers created.

R=horo,mkwst,jochen
BUG=254993

Review URL: https://codereview.chromium.org/594803002

git-svn-id: svn://svn.chromium.org/blink/trunk@182897 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add "debug_devtools" GN build config

This is the Blink-side part of https://codereview.chromium.org/598353003/

R=jochen@chromium.org, jochen, pfeldman

Review URL: https://codereview.chromium.org/618623002

git-svn-id: svn://svn.chromium.org/blink/trunk@182898 bbb929c8-8fbe-4397-9dbb-9b2b20218538