gn: Support build directories outside the source tree.

tools/gn/action_target_generator.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 "tools/gn/action_target_generator.h"
 
 #include "tools/gn/build_settings.h"
 #include "tools/gn/err.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/parse_tree.h"
@@ skipping 55 matching lines @@
   // if it doesn't have one.
   const Value* value = scope_->GetValue(variables::kScript, true);
   if (!value) {
     *err_ = Err(function_call_, "This target type requires a \"script\".");
     return false;
   }
   if (!value->VerifyTypeIs(Value::STRING, err_))
     return false;
 
   SourceFile script_file =
-      scope_->GetSourceDir().ResolveRelativeFile(value->string_value());
+      scope_->GetSourceDir().ResolveRelativeFile(value->string_value(),
+          scope_->settings()->build_settings()->root_path());
   if (script_file.value().empty()) {
     *err_ = Err(*value, "script name is empty");
     return false;
   }
   target_->action_values().set_script(script_file);
   return true;
 }
 
 bool ActionTargetGenerator::FillScriptArgs() {
   const Value* value = scope_->GetValue(variables::kArgs, true);
@@ skipping 40 matching lines @@
       *err_ = Err(function_call_,
           "action_foreach should have a pattern in the output.",
           "An action_foreach target should have a source expansion pattern in\n"
           "it to map source file to unique output file name. Otherwise, the\n"
           "build system can't determine when your script needs to be run.");
       return false;
     }
   }
   return true;
 }