Implement tracking of BUILD.gn files used to define target, toolchain or

tools/gn/analyzer.h

Index: tools/gn/analyzer.h
diff --git a/tools/gn/analyzer.h b/tools/gn/analyzer.h
index 130ebe95ce3447c59f6423169128d31c803a9df6..d3c54cc42e4bca95e675a7722b3c1983631b23ec 100644
--- a/tools/gn/analyzer.h
+++ b/tools/gn/analyzer.h
@@ -24,7 +24,7 @@ class Analyzer {
   using SourceFileSet = std::set<const SourceFile*>;
   using TargetSet = std::set<const Target*>;
 
-  explicit Analyzer(const Builder& builder);
+  Analyzer(const BuildSettings& build_settings, const Builder& builder);
   ~Analyzer();
 
   // Figures out from a Buider and a JSON-formatted string containing lists
@@ -83,6 +83,8 @@ class Analyzer {
 
   void AddAllRefsTo(const Target* target, TargetSet* matches) const;
 
+  bool WereMainGNFilesModified(const SourceFileSet& source_files) const;
+
   std::vector<const Target*> all_targets_;
   std::map<const Label, const Target*> labels_to_targets_;
   Label default_toolchain_;
@@ -90,6 +92,7 @@ class Analyzer {
 
   // Maps targets to the list of targets that depend on them.
   std::multimap<const Target*, const Target*> dep_map_;
+  SourceFile build_config_file_;
 };
 
 #endif  // TOOLS_GN_ANALYZER_H_