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 unregister-and-register-new-script.html.  This must be done as a three-sided patch.

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
NOTREECHECKS=true
NOTRY=true
BUG=398355
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=291092

[falken, 2014-08-21 16:27:39]

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

[commit-bot: I haz the power, 2014-08-21 16:29:26]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/falken@chromium.org/484783003/1

[commit-bot: I haz the power, 2014-08-21 16:33:41]

Committed patchset #1 (1) as 291092