Add forward_variables_from() and target() to GN

tools/gn/target_generator.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/target_generator.h"
 
 #include "tools/gn/action_target_generator.h"
 #include "tools/gn/binary_target_generator.h"
 #include "tools/gn/build_settings.h"
 #include "tools/gn/config.h"
@@ skipping 95 matching lines @@
     generator.Run();
   } else if (output_type == functions::kSourceSet) {
     BinaryTargetGenerator generator(target.get(), scope, function_call,
                                     Target::SOURCE_SET, err);
     generator.Run();
   } else if (output_type == functions::kStaticLibrary) {
     BinaryTargetGenerator generator(target.get(), scope, function_call,
                                     Target::STATIC_LIBRARY, err);
     generator.Run();
   } else {
-    *err = Err(function_call, "Not a known output type",
-               "I am very confused.");
+    *err = Err(function_call, "Not a known target type",
+               "I am very confused by the target type \"" + output_type + "\"");
   }
 
   if (err->has_error())
     return;
 
   // Save this target for the file.
   Scope::ItemVector* collector = scope->GetItemCollector();
   if (!collector) {
     *err = Err(function_call, "Can't define a target in this context.");
     return;
@@ skipping 241 matching lines @@
 bool TargetGenerator::FillForwardDependentConfigs() {
   const Value* value = scope_->GetValue(
       variables::kForwardDependentConfigsFrom, true);
   if (value) {
     ExtractListOfUniqueLabels(*value, scope_->GetSourceDir(),
                               ToolchainLabelForScope(scope_),
                               &target_->forward_dependent_configs(), err_);
   }
   return !err_->has_error();
 }