Add support for reading .gypi files.

tools/gn/scope.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_SCOPE_H_
 #define TOOLS_GN_SCOPE_H_
 
 #include <map>
 #include <set>
 
@@ skipping 132 matching lines @@
   // called before replacing the var with a different one. It does not check
   // containing scopes.
   //
   // If the identifier is present but hasnn't been used, return true.
   bool IsSetButUnused(const base::StringPiece& ident) const;
 
   // Checks the scope to see if any values were set but not used, and fills in
   // the error and returns false if they were.
   bool CheckForUnusedVars(Err* err) const;
 
-  // Returns all values set in the current scope, without going to the parent
-  // scopes.
+  // Returns all key/values or just the keys set in the current scope,
+  // without going to the parent scopes.
   void GetCurrentScopeValues(KeyValueMap* output) const;
+  void GetCurrentScopeKeys(std::vector<base::StringPiece>* output) const;
 
   // Copies this scope's values into the destination. Values from the
   // containing scope(s) (normally shadowed into the current one) will not be
   // copied, neither will the reference to the containing scope (this is why
   // it's "non-recursive").
   //
   // If clobber_existing is true, any existing values will be overwritten. In
   // this mode, this function will never fail.
   //
   // If clobber_existing is false, it will be an error to merge a variable into
@@ skipping 123 matching lines @@
 
   typedef std::set<ProgrammaticProvider*> ProviderSet;
   ProviderSet programmatic_providers_;
 
   SourceDir source_dir_;
 
   DISALLOW_COPY_AND_ASSIGN(Scope);
 };
 
 #endif  // TOOLS_GN_SCOPE_H_