Add an assert_no_deps variable to GN.

tools/gn/value_extractors.h

Index: tools/gn/value_extractors.h
diff --git a/tools/gn/value_extractors.h b/tools/gn/value_extractors.h
index 06d64cef676e78d62fdc0c9c1dfa19f963567739..1e426502036a88724171e4dfe5d5bdc2e3bc9cd8 100644
--- a/tools/gn/value_extractors.h
+++ b/tools/gn/value_extractors.h
@@ -15,6 +15,7 @@
 class BuildSettings;
 class Err;
 class Label;
+class LabelPattern;
 class SourceDir;
 class SourceFile;
 class Value;
@@ -80,4 +81,9 @@ bool ExtractRelativeFile(const BuildSettings* build_settings,
                          SourceFile* file,
                          Err* err);
 
+bool ExtractListOfLabelPatterns(const Value& value,
+                                const SourceDir& current_dir,
+                                std::vector<LabelPattern>* patterns,
+                                Err* err);
+
 #endif  // TOOLS_GN_VALUE_EXTRACTORS_H_