Make WorkerScriptLoader back to RefCounted class

Make WorkerScriptLoader back to RefCounted class

This was made non-refcounted class in https://crrev.com/1190133002,
but looks like this could cause crashes in some corner cases.

To be more specific:
FrameLoaderClientImpl::dispatchDidFinishDocumentLoad() calls
WebFrameClient callback first and then WebView callback next, but
if the loader is deleted in the first callback an attempt to call the
second callback on a member variable would crash.

We could probably avoid this crash without making the loader class
ref-counted again, but for now I would like to fix the crash by simply
reverting some of the changes that're causing the crash.

BUG=524694
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201346

[kinuko, 2015-08-27 08:07:46]

kinuko@chromium.org changed reviewers:
+ ksakamoto@chromium.org, tkent@chromium.org

[kinuko, 2015-08-27 08:10:39]

kinuko@chromium.org changed reviewers:
+ falken@chromium.org

[kinuko, 2015-08-27 08:10:41]

Could you review?

ksakamoto or falken: worker script loader changes
tkent-san: web changes

[Kunihiko Sakamoto, 2015-08-27 08:20:05]

On 2015/08/27 08:10:41, kinuko wrote:
> Could you review?
> 
> ksakamoto or falken: worker script loader changes
> tkent-san: web changes

Could you cc: us on the bug? It gives 403 to me.

[kinuko, 2015-08-27 08:28:28]

On 2015/08/27 08:20:05, Kunihiko Sakamoto wrote:
> On 2015/08/27 08:10:41, kinuko wrote:
> > Could you review?
> > 
> > ksakamoto or falken: worker script loader changes
> > tkent-san: web changes
> 
> Could you cc: us on the bug? It gives 403 to me.

cc-ed all of you.

[Kunihiko Sakamoto, 2015-08-27 08:36:22]

lgtm

[tkent, 2015-08-27 23:25:55]

lgtm

[kinuko, 2015-08-28 00:01:27]

The CQ bit was checked by kinuko@chromium.org

[commit-bot: I haz the power, 2015-08-28 00:01:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1322523002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1322523002/1

[commit-bot: I haz the power, 2015-08-28 00:06:42]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201346