Require build directories exist for some GN commands.

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/timer/elapsed_timer.h"
 #include "tools/gn/build_settings.h"
@@ skipping 59 matching lines @@
 
   if (args.size() != 1) {
     Err(Location(), "Need exactly one build directory to generate.",
         "I expected something more like \"gn gen out/foo\"\n"
         "You can also see \"gn help gen\".").PrintToStdout();
     return 1;
   }
 
   // Deliberately leaked to avoid expensive process teardown.
   Setup* setup = new Setup();
-  if (!setup->DoSetup(args[0]))
+  if (!setup->DoSetup(args[0], true))
     return 1;
 
   if (CommandLine::ForCurrentProcess()->HasSwitch(kSwitchCheck))
     setup->set_check_public_headers(true);
 
   // 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,
@@ skipping 20 matching lines @@
             setup->scheduler().input_file_manager()->GetInputFileCount()) +
         " files in " +
         base::IntToString(elapsed_time.InMilliseconds()) + "ms\n";
     OutputString(stats);
   }
 
   return 0;
 }
 
 }  // namespace commands