Reduce the number of worker threads GN uses.

tools/gn/target.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 "tools/gn/target.h"
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "tools/gn/config_values_extractors.h"
 #include "tools/gn/deps_iterator.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/substitution_writer.h"
+#include "tools/gn/trace.h"
 
 namespace {
 
 typedef std::set<const Config*> ConfigSet;
 
 // Merges the public configs from the given target to the given config list.
 void MergePublicConfigsFrom(const Target* from_target,
                             UniqueVector<LabelConfigPair>* dest) {
   const UniqueVector<LabelConfigPair>& pub = from_target->public_configs();
   dest->Append(pub.begin(), pub.end());
@@ skipping 124 matching lines @@
 }
 
 const Target* Target::AsTarget() const {
   return this;
 }
 
 bool Target::OnResolved(Err* err) {
   DCHECK(output_type_ != UNKNOWN);
   DCHECK(toolchain_) << "Toolchain should have been set before resolving.";
 
+  ScopedTrace trace(TraceItem::TRACE_ON_RESOLVED, label());
+  trace.SetToolchain(settings()->toolchain_label());
+
   // Copy our own dependent configs to the list of configs applying to us.
   configs_.Append(all_dependent_configs_.begin(), all_dependent_configs_.end());
   MergePublicConfigsFrom(this, &configs_);
 
   // Copy our own libs and lib_dirs to the final set. This will be from our
   // target and all of our configs. We do this specially since these must be
   // inherited through the dependency tree (other flags don't work this way).
   for (ConfigValuesIterator iter(this); !iter.done(); iter.Next()) {
     const ConfigValues& cur = iter.cur();
     all_lib_dirs_.append(cur.lib_dirs().begin(), cur.lib_dirs().end());
@@ skipping 372 matching lines @@
     return;  // Not in output dir, this is OK.
 
   // Tell the scheduler about unknown files. This will be noted for later so
   // the list of files written by the GN build itself (often response files)
   // can be filtered out of this list.
   OutputFile out_file(settings()->build_settings(), source);
   std::set<const Target*> seen_targets;
   if (!EnsureFileIsGeneratedByDependency(this, out_file, true, &seen_targets))
     g_scheduler->AddUnknownGeneratedInput(this, source);
 }