Make use of ElapsedTimer API for the 'gen' command.

tools/gn/command_gen.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 "base/atomicops.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/strings/string_number_conversions.h"
-#include "base/time/time.h"
+#include "base/timer/elapsed_timer.h"
 #include "tools/gn/build_settings.h"
 #include "tools/gn/commands.h"
 #include "tools/gn/ninja_target_writer.h"
 #include "tools/gn/ninja_writer.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/setup.h"
 #include "tools/gn/standard_out.h"
 
 namespace commands {
 
@@ skipping 30 matching lines @@
 const char kGen_HelpShort[] =
     "gen: Generate ninja files.";
 const char kGen_Help[] =
     "gn gen\n"
     "  Generates ninja files from the current tree.\n"
     "\n"
     "  See \"gn help\" for the common command-line switches.\n";
 
 // Note: partially duplicated in command_gyp.cc.
 int RunGen(const std::vector<std::string>& args) {
-  base::TimeTicks begin_time = base::TimeTicks::Now();
+  base::ElapsedTimer timer;
 
   // Deliberately leaked to avoid expensive process teardown.
   Setup* setup = new Setup;
   if (!setup->DoSetup())
     return 1;
 
   // Cause the load to also generate the ninja files for each target. We wrap
   // the writing to maintain a counter.
   base::subtle::Atomic32 write_counter = 0;
   setup->builder()->set_resolved_callback(
       base::Bind(&ItemResolvedCallback, &write_counter,
                  scoped_refptr<Builder>(setup->builder())));
 
   // Do the actual load. This will also write out the target ninja files.
   if (!setup->Run())
     return 1;
 
   // Write the root ninja files.
   if (!NinjaWriter::RunAndWriteFiles(&setup->build_settings(),
                                      setup->builder()))
     return 1;
 
-  base::TimeTicks end_time = base::TimeTicks::Now();
+  base::TimeDelta elapsed_time = timer.Elapsed();
 
   if (!CommandLine::ForCurrentProcess()->HasSwitch(kSwitchQuiet)) {
     OutputString("Done. ", DECORATION_GREEN);
 
     std::string stats = "Wrote " +
         base::IntToString(static_cast<int>(write_counter)) +
         " targets from " +
         base::IntToString(
             setup->scheduler().input_file_manager()->GetInputFileCount()) +
         " files in " +
-        base::IntToString((end_time - begin_time).InMilliseconds()) + "ms\n";
+        base::IntToString(elapsed_time.InMilliseconds()) + "ms\n";
     OutputString(stats);
   }
 
   return 0;
 }
 
 }  // namespace commands