Add more instrumentation to track down jank.

net/proxy/proxy_resolver_v8_tracing.cc

Index: net/proxy/proxy_resolver_v8_tracing.cc
diff --git a/net/proxy/proxy_resolver_v8_tracing.cc b/net/proxy/proxy_resolver_v8_tracing.cc
index c498f749bb6e8163a2dab165a7cf88c9dea0ddee..31e849076e2037b7de72b82bfe5871a767fce555 100644
--- a/net/proxy/proxy_resolver_v8_tracing.cc
+++ b/net/proxy/proxy_resolver_v8_tracing.cc
@@ -939,6 +939,11 @@ ProxyResolverV8Tracing::ProxyResolverV8Tracing(
       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"));