Replace a CHECK in the socket pool code with a NOTREACHED().

net/socket/client_socket_pool_base.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/socket/client_socket_pool_base.h"
 
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 545 matching lines @@
   return i->second->idle_sockets().size();
 }
 
 LoadState ClientSocketPoolBaseHelper::GetLoadState(
     const std::string& group_name,
     const ClientSocketHandle* handle) const {
   if (ContainsKey(pending_callback_map_, handle))
     return LOAD_STATE_CONNECTING;
 
   GroupMap::const_iterator group_it = group_map_.find(group_name);
-  // TODO(mmenke):  Switch to DCHECK once sure this doesn't break anything.
-  //     Added in M43.
-  CHECK(group_it != group_map_.end());
+  if (group_it == group_map_.end()) {
+    // TODO(mmenke):  This is actually reached in the wild, for unknown reasons.
+    // Would be great to understand why, and if it's a bug, fix it.  If not,
+    // should have a test for that case.
+    NOTREACHED();
+    return LOAD_STATE_IDLE;
+  }
+
   const Group& group = *group_it->second;
-
   if (group.HasConnectJobForHandle(handle)) {
     // Just return the state of the farthest along ConnectJob for the first
     // group.jobs().size() pending requests.
     LoadState max_state = LOAD_STATE_IDLE;
     for (const auto& job : group.jobs()) {
       max_state = std::max(max_state, job->GetLoadState());
     }
     return max_state;
   }
 
@@ skipping 749 matching lines @@
   pending_requests_.Erase(pointer);
   // If there are no more requests, kill the backup timer.
   if (pending_requests_.empty())
     backup_job_timer_.Stop();
   return request.Pass();
 }
 
 }  // namespace internal
 
 }  // namespace net