Add testonly flag to GN

tools/gn/item.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_ITEM_H_
 #define TOOLS_GN_ITEM_H_
 
 #include <string>
 
 #include "tools/gn/label.h"
@@ skipping 30 matching lines @@
   virtual Target* AsTarget();
   virtual const Target* AsTarget() const;
   virtual Toolchain* AsToolchain();
   virtual const Toolchain* AsToolchain() const;
 
   // Returns a name like "target" or "config" for the type of item this is, to
   // be used in logging and error messages.
   std::string GetItemTypeName() const;
 
   // Called when this item is resolved, meaning it and all of its dependents
-  // have no unresolved deps.
-  virtual void OnResolved() {}
+  // have no unresolved deps. Returns true on success. Sets the error and
+  // returns false on failure.
+  virtual bool OnResolved(Err* err);
 
  private:
   const Settings* settings_;
   Label label_;
   const ParseNode* defined_from_;
 
   Visibility visibility_;
 };
 
 #endif  // TOOLS_GN_ITEM_H_