Revert of Service Worker: Handle same-scope, new script registration

Revert of Service Worker: Handle same-scope, new script registration (patchset #8 of https://codereview.chromium.org/472103003/)

Reason for revert:
Broke http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=@ToT%20Blink&tests=http%2Ftests%2Fserviceworker%2Funregister-then-register-new-script.html&testType=layout-tests

Original issue's description:
> Service Worker: Handle same-scope, new script registration
> 
> Before this patch, register() would delete an existing registration at
> the scope if the script URL didn't match, and register a new one. This
> overwriting creates a scenario where old tabs have a different
> controller than new tabs, which the Service Worker spec avoids.
> 
> This patch implements the spec steps for same-scope, new script
> register(). That means:
> 
> - If the existing registration is uninstalling, wait for that to
> complete before doing anything.
> - Create a new worker which becomes the installing worker of the
> existing registration.
> 
> BUG=398355
> TEST=https://codereview.chromium.org/480943002/
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=291078

TBR=michaeln@chromium.org,nhiroki@chromium.org,falken@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=398355

[dglazkov, 2014-08-21 16:30:42]

Created Revert of Service Worker: Handle same-scope, new script registration

[falken, 2014-08-21 16:32:11]

The CQ bit was unchecked by falken@chromium.org

[falken, 2014-08-21 16:32:37]

On 2014/08/21 16:32:11, falken wrote:
> The CQ bit was unchecked by mailto:falken@chromium.org

(Already have a revert at https://codereview.chromium.org/484783003/)

[dglazkov, 2014-08-21 16:34:49]

On 2014/08/21 at 16:32:37, falken wrote:
> On 2014/08/21 16:32:11, falken wrote:
> > The CQ bit was unchecked by mailto:falken@chromium.org
> 
> (Already have a revert at https://codereview.chromium.org/484783003/)

LOL! :)