Delete EmbeddedWorkerDispatcher in RenderThreadImpl::Shutdown().

Delete EmbeddedWorkerDispatcher in RenderThreadImpl::Shutdown().

In current code, EmbeddedWorkerDispatcher is deleted in the destructor of RenderThreadImpl.
If EmbeddedWorkerDispatcher contains any WorkerWrapper in workers_, WorkerWrapper and EmbeddedWorkerDevToolsAgent will be deleted at that time.
And the destructor of EmbeddedWorkerDevToolsAgent will call RemoveEmbeddedWorkerRoute of RenderThreadImpl which is being deleted.

To avoid this we should delete EmbeddedWorkerDispatcher in RenderThreadImpl::Shutdown().

BUG=377258, 358657
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272892

[horo, 2014-05-26 04:19:15]

falken@
Could you please review?

[falken, 2014-05-26 04:59:11]

On 2014/05/26 04:19:15, horo wrote:
> falken@
> Could you please review?

lgtm. I don't know shutdown so well but CL description and code makes sense. How
about a comment like the IDB one below this?

[horo, 2014-05-26 05:38:53]

On 2014/05/26 04:59:11, falken wrote:
> On 2014/05/26 04:19:15, horo wrote:
> > falken@
> > Could you please review?
> 
> lgtm. I don't know shutdown so well but CL description and code makes sense.
How
> about a comment like the IDB one below this?

Done.
Added comment.

[horo, 2014-05-26 05:39:36]

jochen@
Could you please review this?

[jochen (gone - plz use gerrit), 2014-05-26 09:56:46]

lgtm

[horo, 2014-05-26 16:04:49]

The CQ bit was checked by horo@chromium.org

[commit-bot: I haz the power, 2014-05-26 16:07:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/horo@chromium.org/297343002/20001

[commit-bot: I haz the power, 2014-05-27 00:03:00]

Change committed as 272892