GN: Use the correct defaults for templates invoked via target().

tools/gn/template.h

 // Copyright 2014 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_TEMPLATE_H_
 #define TOOLS_GN_TEMPLATE_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 15 matching lines @@
 // execute the template in parallel.
 class Template : public base::RefCountedThreadSafe<Template> {
  public:
   // Makes a new closure based on the given scope.
   Template(const Scope* scope, const FunctionCallNode* def);
 
   // Takes ownership of a previously-constructed closure.
   Template(std::unique_ptr<Scope> closure, const FunctionCallNode* def);
 
   // Invoke the template. The values correspond to the state of the code
-  // invoking the template.
+  // invoking the template. The template name needs to be supplied since the
+  // template object itself doesn't know what name the calling code is using
+  // to refer to it (this is used to set defaults).
   Value Invoke(Scope* scope,
                const FunctionCallNode* invocation,
+               const std::string& template_name,
                const std::vector<Value>& args,
                BlockNode* block,
                Err* err) const;
 
   // Returns the location range where this template was defined.
   LocationRange GetDefinitionRange() const;
 
  private:
   friend class base::RefCountedThreadSafe<Template>;
 
   Template();
   ~Template();
 
   std::unique_ptr<Scope> closure_;
   const FunctionCallNode* definition_;
 };
 
 #endif  // TOOLS_GN_TEMPLATE_H_