GN: Make file/dir resolving return errors.

tools/gn/value_extractors.cc

Index: tools/gn/value_extractors.cc
diff --git a/tools/gn/value_extractors.cc b/tools/gn/value_extractors.cc
index 6dfaa2f677e35ff5c315896826e292dc2fdae885..365c5342779c841b79e34337ff6cc4a93c7a1add 100644
--- a/tools/gn/value_extractors.cc
+++ b/tools/gn/value_extractors.cc
@@ -65,11 +65,9 @@ struct RelativeFileConverter {
         current_dir(current_dir_in) {
   }
   bool operator()(const Value& v, SourceFile* out, Err* err) const {
-    if (!v.VerifyTypeIs(Value::STRING, err))
-      return false;
-    *out = current_dir.ResolveRelativeFile(v.string_value(),
+    *out = current_dir.ResolveRelativeFile(v, err,
                                            build_settings->root_path_utf8());
-    return true;
+    return !err->has_error();
   }
   const BuildSettings* build_settings;
   const SourceDir& current_dir;
@@ -82,9 +80,7 @@ struct RelativeDirConverter {
         current_dir(current_dir_in) {
   }
   bool operator()(const Value& v, SourceDir* out, Err* err) const {
-    if (!v.VerifyTypeIs(Value::STRING, err))
-      return false;
-    *out = current_dir.ResolveRelativeDir(v.string_value(),
+    *out = current_dir.ResolveRelativeDir(v, err,
                                           build_settings->root_path_utf8());
     return true;
   }