Add TaskPriority as a parameter to SequencedWorkerPool in preparation for TaskScheduler experiment.

net/proxy/dhcp_proxy_script_fetcher_win.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/proxy/dhcp_proxy_script_fetcher_win.h"
 
 #include <memory>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 40 matching lines @@
 namespace net {
 
 DhcpProxyScriptFetcherWin::DhcpProxyScriptFetcherWin(
     URLRequestContext* url_request_context)
     : state_(STATE_START),
       num_pending_fetchers_(0),
       destination_string_(NULL),
       url_request_context_(url_request_context) {
   DCHECK(url_request_context_);
 
-  worker_pool_ = new base::SequencedWorkerPool(kMaxDhcpLookupThreads,
-                                               "PacDhcpLookup");
+  worker_pool_ =
+      new base::SequencedWorkerPool(kMaxDhcpLookupThreads, "PacDhcpLookup",

[eroman, 2016/06/23 01:19:21]

BTW I don't believe this actually has any ordering requirements.

Looks like it is just using the maximum threads parameter to rate limit the
requests made, could be changed to ExecutionMode:PARALLEL in the future.

[gab, 2016/06/27 21:29:32]

Ack, will keep in mind for later, thanks!

+                                    base::TaskPriority::USER_BLOCKING);

[eroman, 2016/06/23 01:19:21]

USER_VISIBLE should be good enough for this.

As an aside, I wonder if just these 3 priority classes will be sufficiently
granular to make good scheduling choices.

Here for instance after the transition we could just be firing off all the tasks
with ExecutionMode::PARALLEL and priority=USER_VISIBLE.

That is fine, but in theory we have more information available. Some of the
tasks (adapter probes) are less important than others and could be
de-prioritized. But not so unimportant as to become BACKGROUND.

This particular case isn't all that interesting (wasn't really optimized
before), but still curious if there are plans to have more priorities or other
ways to describe precedence of tasks than those 3.

[gab, 2016/06/27 21:29:32]

Done.
Interesting, filed http://crbug.com/623683 to consider this.

 }
 
 DhcpProxyScriptFetcherWin::~DhcpProxyScriptFetcherWin() {
   // Count as user-initiated if we are not yet in STATE_DONE.
   Cancel();
 
   worker_pool_->Shutdown();
 }
 
 int DhcpProxyScriptFetcherWin::Fetch(base::string16* utf16_text,
@@ skipping 301 matching lines @@
 
 bool DhcpProxyScriptFetcherWin::AdapterQuery::ImplGetCandidateAdapterNames(
     std::set<std::string>* adapter_names) {
   return DhcpProxyScriptFetcherWin::GetCandidateAdapterNames(adapter_names);
 }
 
 DhcpProxyScriptFetcherWin::AdapterQuery::~AdapterQuery() {
 }
 
 }  // namespace net