Use paths relative to build dir in custom actions.

tools/gn/ninja_script_target_writer.cc

Index: tools/gn/ninja_script_target_writer.cc
diff --git a/tools/gn/ninja_script_target_writer.cc b/tools/gn/ninja_script_target_writer.cc
index 4678ba05f43ea039f43686455c45fd6a1b7ec560..e5af560d74fdfbe04fbedecf0974ce9bf6665324 100644
--- a/tools/gn/ninja_script_target_writer.cc
+++ b/tools/gn/ninja_script_target_writer.cc
@@ -92,10 +92,7 @@ std::string NinjaScriptTargetWriter::WriteRuleDefinition(
   } else {
     // Posix can execute Python directly.
     out_ << "rule " << custom_rule_name << std::endl;
-    out_ << "  command = cd ";
-    path_output_.WriteDir(out_, target_->label().dir(),
-                          PathOutput::DIR_NO_LAST_SLASH);
-    out_ << "; $pythonpath ";
+    out_ << "  command = $pythonpath ";

[brettw, 2013/10/23 16:27:05]

While you're here, can you do WriteFile(...python_path() like we do above? I
used to use $pythonpath everywhere but this was causing problems with the GYP
integration so I'm moving to writing the path out.

[koz (OOO until 15th September), 2013/10/24 05:56:28]

Done.

     path_output_.WriteFile(out_, target_->script_values().script());
     args_template.WriteWithNinjaExpansions(out_);
     out_ << std::endl;
@@ -133,7 +130,7 @@ void NinjaScriptTargetWriter::WriteSourceRules(
     out_ << "build";
     WriteOutputFilesForBuildLine(output_template, sources[i], output_files);
 
-    out_ << ": " << custom_rule_name;
+    out_ << ": " << custom_rule_name << " ";

[brettw, 2013/10/23 16:27:05]

Whoopsies! I guess I haven't done any script stuff lately.

[koz (OOO until 15th September), 2013/10/24 05:56:28]

I wondered for a bit if it was some bit of ninja syntax I hadn't yet seen :-)

     path_output_.WriteFile(out_, sources[i]);
     out_ << implicit_deps << std::endl;