Add testonly flag to GN

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>
 
 #include "tools/gn/label.h"
@@ skipping 18 matching lines @@
 
   // 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.
+
+  // The origin of this dependency. This will be null for internally generated
+  // dependencies. This happens when a group is automatically expanded and that
+  // group's members are added to the target that depends on that group.
+  const ParseNode* origin;
 };
 
 typedef LabelPtrPair<Config> LabelConfigPair;
 typedef LabelPtrPair<Target> LabelTargetPair;
 
 typedef std::vector<LabelConfigPair> LabelConfigVector;
 typedef std::vector<LabelTargetPair> LabelTargetVector;
 
 // Comparison and search functions ---------------------------------------------
 
@@ skipping 61 matching lines @@
 #elif defined(COMPILER_MSVC)
 template<typename T>
 inline size_t hash_value(const LabelPtrPair<T>& v) {
   return BASE_HASH_NAMESPACE::hash_value(v.label);
 }
 #endif  // COMPILER...
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // TOOLS_GN_LABEL_PTR_H_