Fix GN unit tests

tools/gn/function_exec_script.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/command_line.h"
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/process/kill.h"
 #include "base/process/launch.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 330 matching lines @@
 #if defined(OS_WIN)
     g_scheduler->Log("Pythoning", UTF16ToUTF8(cmdline.GetCommandLineString()));
 #else
     g_scheduler->Log("Pythoning", cmdline.GetCommandLineString());
 #endif
     begin_exec = base::TimeTicks::Now();
   }
 
   base::FilePath startup_dir =
       build_settings->GetFullPath(build_settings->build_dir());
+  // The first time a build is run, no targets will have been written so the
+  // build output directory won't exist. We need to make sure it does before
+  // running any scripts with this as its startup directory, although it will
+  // be relatively rare that the directory won't exist by the time we get here.
+  //
+  // If this shows up on benchmarks, we can cache whether we've done this
+  // or not and skip creating the directory.
+  file_util::CreateDirectory(startup_dir);

[scottmg, 2013/10/24 21:47:20]

racing is silently ok on all platforms? (looks ok on windows, but i didn't check
all of them)

 
   // Execute the process.
   // TODO(brettw) set the environment block.
   std::string output;
   std::string stderr_output;  // TODO(brettw) not hooked up, see above.
   int exit_code = 0;
   if (!CommandLine::ForCurrentProcess()->HasSwitch(kNoExecSwitch)) {
     if (!ExecProcess(cmdline, startup_dir,
                      &output, &stderr_output, &exit_code)) {
       *err = Err(function->function(), "Could not execute python.",
@@ skipping 19 matching lines @@
       msg += ".";
     *err = Err(function->function(), "Script returned non-zero exit code.",
                msg);
     return Value();
   }
 
   return ConvertInputToValue(output, function, args[2], err);
 }
 
 }  // namespace functions