Fix GN unit tests

tools/gn/function_exec_script.cc

Index: tools/gn/function_exec_script.cc
diff --git a/tools/gn/function_exec_script.cc b/tools/gn/function_exec_script.cc
index 540d189069aae8803d5aa2c316637bd7bca0b95c..bf55165ea4f975f7e2e1c5b0887917d89b4b7fae 100644
--- a/tools/gn/function_exec_script.cc
+++ b/tools/gn/function_exec_script.cc
@@ -348,6 +348,14 @@ Value RunExecScript(Scope* scope,
 
   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.