Revert of Add a crash-hunting CHECK() in RenderProcessHostImpl::AddRoute()...

Revert of Add a crash-hunting CHECK() in RenderProcessHostImpl::AddRoute() (patchset #1 id:1 of https://codereview.chromium.org/647623003/)

Reason for revert:
per bug https://code.google.com/p/chromium/issues/detail?id=422694 a bunch of crashes both in mac and windows today's canary.

Original issue's description:
> Add a crash-hunting CHECK() in RenderProcessHostImpl::AddRoute()
>
> This is an equivalent of DCHECK() in IDMap.
> According to crbug.com/381990, this can occasionally crash.
> I'd like to enable this to collect more data if it still crashes.
> If you see this CHECK() being hit in the wild,
> please revert this change and let me know.
>
> BUG=381990, 415059
> R=nasko@chromium.org, amineer@chromium.org
>
> Committed: https://crrev.com/9a8e3d71f73ace82874d53ba2e749b1173a98513
> Cr-Commit-Position: refs/heads/master@{#299146}

TBR=amineer@chromium.org,nasko@chromium.org,karen@chromium.org,morrita@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=381990, 415059

Review URL: https://codereview.chromium.org/645233003

Cr-Commit-Position: refs/heads/master@{#299248}

content/browser/renderer_host/render_process_host_impl.cc

@@ -920,9 +920,6 @@ ServiceRegistry* RenderProcessHostImpl::GetServiceRegistry() {
 void RenderProcessHostImpl::AddRoute(
     int32 routing_id,
     IPC::Listener* listener) {
-  // We already have DCHECK() in IDMap. This is for chasing
-  // crbug.com/415059 and can be removed after fixing it.
-  CHECK(!listeners_.Lookup(routing_id));
   listeners_.AddWithID(listener, routing_id);
 }