Revert of Blink: Adds a mechanism to pause the serviceworker startup sequence (https://codereview.chromium.org/339703006/)

Reason for revert:
Speculative revert. The following started flakily timing out around this patch:

virtual/serviceworker/http/tests/serviceworker/registration.html
virtual/serviceworker/http/tests/serviceworker/serviceworkerobject-scope.html

Also win blink rel trybot has massive serviceworker failures on unrelated patches, e.g.,:
http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/12803
http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/12802

Original issue's description:
> Blink: Adds a mechanism to pause the serviceworker startup sequence after downloading the main script and then to resume. This is to give the browser process a chance to compare the old and new script during a softupdate. 
> 
> BUG=371671
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176552

TBR=jochen@chromium.org,michaeln@google.com,michaeln@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=371671

Review URL: https://codereview.chromium.org/344833007

git-svn-id: svn://svn.chromium.org/blink/trunk@176588 bbb929c8-8fbe-4397-9dbb-9b2b20218538