Document GN invoker and target name variables.

tools/gn/functions.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/functions.h"
 
 #include <stddef.h>
 #include <iostream>
 #include <utility>
 
@@ skipping 83 matching lines @@
                                             function, "target defaults", err))
       return false;
   }
 
   // The name is the single argument to the target function.
   if (!EnsureSingleStringArg(function, args, err))
     return false;
 
   // Set the target name variable to the current target, and mark it used
   // because we don't want to issue an error if the script ignores it.
-  const base::StringPiece target_name("target_name");
+  const base::StringPiece target_name(variables::kTargetName);
   block_scope->SetValue(target_name, Value(function, args[0].string_value()),
                         function);
   block_scope->MarkUsed(target_name);
   return true;
 }
 
 void FillNeedsBlockError(const FunctionCallNode* function, Err* err) {
   *err = Err(function->function(), "This function call requires a block.",
       "The block's \"{\" must be on the same line as the function "
       "call's \")\".");
@@ skipping 983 matching lines @@
   }
 
   // Otherwise it's a no-block function.
   if (!VerifyNoBlockForFunctionCall(function, block, err))
     return Value();
   return found_function->second.no_block_runner(scope, function,
                                                 args.list_value(), err);
 }
 
 }  // namespace functions