Update FinalizeVmRegionDumpIfAllManagersReplied to remove DCHECK.

It's possible for no request to exist if the client process is unregistered
around the same time that the MemoryDumpResponse is comes in.

Change-Id: Ib68dd98e076047ddbd6cc7efef58951746c8ad9b
TBR: primiano@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/935321Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538938}

services/resource_coordinator/memory_instrumentation/coordinator_impl.cc

@@ -479,7 +479,9 @@ void CoordinatorImpl::FinalizeVmRegionDumpIfAllManagersReplied(
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
 
   auto it = in_progress_vm_region_requests_.find(dump_guid);
-  DCHECK(it != in_progress_vm_region_requests_.end());
+  if (it == in_progress_vm_region_requests_.end())
+    return;
+
   if (!it->second->pending_responses.empty())
     return;