GN threading refactor

tools/gn/label_ptr.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_LABEL_PTR_H_
 #define TOOLS_GN_LABEL_PTR_H_
 
 #include <functional>
 
 class ParseNode;
 
 // Structure that holds a labeled "thing". This is used for various places
 // where we need to store lists of targets or configs. We sometimes populate
 // the pointers on another thread from where we compute the labels, so this
 // structure lets us save them separately. This also allows us to store the
 // location of the thing that added this dependency.
 template<typename T>
 struct LabelPtrPair {
   typedef T DestType;
 
   LabelPtrPair() : label(), ptr(NULL), origin(NULL) {}
 
+  explicit LabelPtrPair(const Label& l) : label(l), ptr(NULL), origin(NULL) {
+  }
+
   // This contructor is typically used in unit tests, it extracts the label
   // automatically from a given pointer.
   explicit LabelPtrPair(const T* p) : label(p->label()), ptr(p), origin(NULL) {
   }
 
   ~LabelPtrPair() {}
 
   Label label;
   const T* ptr;  // May be NULL.
   const ParseNode* origin;  // May be NULL.
@@ skipping 38 matching lines @@
 template<typename T>
 struct LabelPtrLabelLess : public std::binary_function<LabelPtrPair<T>,
                                                        LabelPtrPair<T>,
                                                        bool> {
   bool operator()(const LabelPtrPair<T>& a, const LabelPtrPair<T>& b) const {
     return a.label < b.label;
   }
 };
 
 #endif  // TOOLS_GN_LABEL_PTR_H_