Guarantee ServiceWorkerCacheStorage::LazyInit calls its callback

Guarantee LazyInit calls its callback by making the callbacks static and passing a WeakPtr to CacheStorage to the callback instead.

Part of the following CL chain to guarantee callbacks are called throughout ServiceWorkerCacheStorage:

1. Guarantee CacheLoader callbacks: https://codereview.chromium.org/504233003/
* 2. Guarantee LazyInit callbacks: https://codereview.chromium.org/512743002/
3. Guarantee Create/Delete callbacks: https://codereview.chromium.org/511893002/
4. Reorganize the methods: https://codereview.chromium.org/510813002/

BUG=392621

[jkarlin, 2014-08-27 14:47:38]

jkarlin@chromium.org changed reviewers:
+ michaeln@chromium.org

[jkarlin, 2014-08-27 14:47:38]

michaeln: Please review all.  Thanks!

[jkarlin, 2014-08-27 16:12:04]

jkarlin@chromium.org changed reviewers:
+ horo@chromium.org

[jkarlin, 2014-08-27 16:15:17]

On 2014/08/27 16:12:04, jkarlin wrote:
> mailto:jkarlin@chromium.org changed reviewers:
> + mailto:horo@chromium.org

horo + michaeln: Please review all, thanks!

[michaeln, 2014-08-27 22:00:54]

https://codereview.chromium.org/512743002/diff/60001/content/browser/service_...
File content/browser/service_worker/service_worker_cache_storage.cc (right):

https://codereview.chromium.org/512743002/diff/60001/content/browser/service_...
content/browser/service_worker/service_worker_cache_storage.cc:417: it->Run();
This doesn't look quite right. The set of possible init_callbacks are these
intsance methods: CreateCache(), GetCache(), EnumerateCaches(). Looks like those
methods will append another callback to themselve since the class is still
!initialized_ at this time, and this loop may never terminate.

Maybe i'm missing something?

Invoking client callbacks from the dtor is dicey since the callback may invoke
another public method of this class.

[jkarlin, 2014-08-28 11:03:16]

jkarlin@chromium.org changed reviewers:
- horo@chromium.org, michaeln@chromium.org

[jkarlin, 2014-08-28 11:05:16]

On 2014/08/28 11:03:16, jkarlin wrote:
> mailto:jkarlin@chromium.org changed reviewers:
> - mailto:horo@chromium.org, mailto:michaeln@chromium.org

Removed reviewers as this patch isn't required and adds complexity.