Add support for reading .gypi files.

tools/gn/scope.cc

 // 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.
 
 #include "tools/gn/scope.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/template.h"
@@ skipping 174 matching lines @@
     }
   }
   return true;
 }
 
 void Scope::GetCurrentScopeValues(KeyValueMap* output) const {
   for (RecordMap::const_iterator i = values_.begin(); i != values_.end(); ++i)
     (*output)[i->first] = i->second.value;
 }
 
+void Scope::GetCurrentScopeKeys(std::vector<base::StringPiece>* output) const {
+  for (RecordMap::const_iterator i = values_.begin(); i != values_.end(); ++i)
+    output->push_back(i->first);
+}
+
 bool Scope::NonRecursiveMergeTo(Scope* dest,
                                 bool clobber_existing,
                                 const ParseNode* node_for_err,
                                 const char* desc_for_err,
                                 Err* err) const {
   // Values.
   for (RecordMap::const_iterator i = values_.begin(); i != values_.end(); ++i) {
     const Value& new_value = i->second.value;
     if (!clobber_existing) {
       const Value* existing_value = dest->GetValue(i->first);
@@ skipping 207 matching lines @@
 }
 
 void Scope::AddProvider(ProgrammaticProvider* p) {
   programmatic_providers_.insert(p);
 }
 
 void Scope::RemoveProvider(ProgrammaticProvider* p) {
   DCHECK(programmatic_providers_.find(p) != programmatic_providers_.end());
   programmatic_providers_.erase(p);
 }