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

tools/gn/scope.h

Index: tools/gn/scope.h
diff --git a/tools/gn/scope.h b/tools/gn/scope.h
index 31bac6261464826a3bd069b3dd7d87ba5f5eaeba..377bb70b2ce066455247adea6a752ceae03114bd 100644
--- a/tools/gn/scope.h
+++ b/tools/gn/scope.h
@@ -99,7 +99,8 @@ class Scope {
   };
 
   // Creates an empty toplevel scope.
-  explicit Scope(const Settings* settings);
+  Scope(const Settings* settings,
+        const std::set<uint32_t>& source_files_hashes);

[brettw, 2017/06/27 00:50:40]

I believe a base::flat_set<uint32_t> will be more efficient in this use. set
will allocate for every insertion which will slow it down, and I suspect moving
ints for insertion will be much faster than a heap allocation. This will also be
much faster for making copies of the set (one allocation rather than N) which it
looks like the patch does a lot.

Maybe we want a typedef for this.

[alex-ac, 2017/06/27 13:46:31]

Done.

 
   // Creates a dependent scope.
   explicit Scope(Scope* parent);
@@ -283,6 +284,12 @@ class Scope {
   const SourceDir& GetSourceDir() const;
   void set_source_dir(const SourceDir& d) { source_dir_ = d; }
 
+  // The set of source files which affected this scope.
+  const std::set<uint32_t>& source_files_hashes() const {
+    return source_files_hashes_;
+  }
+  void AddSourceFile(const SourceFile& source_file);
+
   // The item collector is where Items (Targets, Configs, etc.) go that have
   // been defined. If a scope can generate items, this non-owning pointer will
   // point to the storage for such items. The creator of this scope will be
@@ -378,6 +385,8 @@ class Scope {
 
   SourceDir source_dir_;
 
+  std::set<uint32_t> source_files_hashes_;
+
   DISALLOW_COPY_AND_ASSIGN(Scope);
 };