Add an assert_no_deps variable to GN.

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 23c5a2726dc8f8c78c4f11ca74a3b06bc4de41ff..ff009ce1b59e044ae97fe69157b3f40df965bab5 100644
--- a/tools/gn/value_extractors.cc
+++ b/tools/gn/value_extractors.cc
@@ -144,6 +144,17 @@ template<typename T> struct LabelPtrResolver {
   const Label& current_toolchain;
 };
 
+struct LabelPatternResolver {
+  LabelPatternResolver(const SourceDir& current_dir_in)
+      : current_dir(current_dir_in) {
+  }
+  bool operator()(const Value& v, LabelPattern* out, Err* err) const {
+    *out = LabelPattern::GetPattern(current_dir, v, err);
+    return !err->has_error();
+  }
+  const SourceDir& current_dir;
+};
+
 }  // namespace
 
 bool ExtractListOfStringValues(const Value& value,
@@ -236,3 +247,11 @@ bool ExtractRelativeFile(const BuildSettings* build_settings,
   RelativeFileConverter converter(build_settings, current_dir);
   return converter(value, file, err);
 }
+
+bool ExtractListOfLabelPatterns(const Value& value,
+                                const SourceDir& current_dir,
+                                std::vector<LabelPattern>* patterns,
+                                Err* err) {
+  return ListValueExtractor(value, patterns, err,
+                            LabelPatternResolver(current_dir));
+}