Add more instrumentation to track down jank.

net/proxy/proxy_resolver_v8_tracing.cc

 // Copyright (c) 2013 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/proxy_resolver_v8_tracing.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/stringprintf.h"
@@ skipping 921 matching lines @@
 
 ProxyResolverV8Tracing::ProxyResolverV8Tracing(
     HostResolver* host_resolver,
     ProxyResolverErrorObserver* error_observer,
     NetLog* net_log)
     : ProxyResolver(true /*expects_pac_bytes*/),
       host_resolver_(host_resolver),
       error_observer_(error_observer),
       net_log_(net_log),
       num_outstanding_callbacks_(0) {
+  // TODO(eroman): Remove once crbug.com/454983 is fixed.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "454983 ProxyResolverV8Tracing::ProxyResolverV8Tracing"));
+
   DCHECK(host_resolver);
   // Start up the thread.
   thread_.reset(new base::Thread("Proxy resolver"));
   base::Thread::Options options;
   options.timer_slack = base::TIMER_SLACK_MAXIMUM;
   CHECK(thread_->StartWithOptions(options));

[eroman, 2015/03/06 22:22:43]

My working theory is that starting the thread is the janky action. However I
instrumented in other places just in case that theory is wrong, so I don't have
to wait for yet another canary release.

[mmenke, 2015/03/06 22:56:44]

SGTM

 
   v8_resolver_.reset(new ProxyResolverV8);
 }
 
 ProxyResolverV8Tracing::~ProxyResolverV8Tracing() {
   // Note, all requests should have been cancelled.
   CHECK(!set_pac_script_job_.get());
   CHECK_EQ(0, num_outstanding_callbacks_);
 
   // Join the worker thread. See http://crbug.com/69710. Note that we call
@@ skipping 49 matching lines @@
   DCHECK(!set_pac_script_job_.get());
   CHECK_EQ(0, num_outstanding_callbacks_);
 
   set_pac_script_job_ = new Job(this);
   set_pac_script_job_->StartSetPacScript(script_data, callback);
 
   return ERR_IO_PENDING;
 }
 
 }  // namespace net