Add testonly flag to GN

tools/gn/builder.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/builder.h"
 
 #include "tools/gn/config.h"
 #include "tools/gn/err.h"
 #include "tools/gn/loader.h"
 #include "tools/gn/scheduler.h"
@@ skipping 400 matching lines @@
         !ResolveForwardDependentConfigs(target, err) ||
         !ResolveToolchain(target, err))
       return false;
   } else if (record->type() == BuilderRecord::ITEM_TOOLCHAIN) {
     Toolchain* toolchain = record->item()->AsToolchain();
     if (!ResolveDeps(&toolchain->deps(), err))
       return false;
   }
 
   record->set_resolved(true);
-  record->item()->OnResolved();
+
+  if (!record->item()->OnResolved(err))
+    return false;
   if (!resolved_callback_.is_null())
     resolved_callback_.Run(record);
 
   // Recursively update everybody waiting on this item to be resolved.
   BuilderRecordSet& waiting_set = record->waiting_on_resolution();
   for (BuilderRecordSet::iterator i = waiting_set.begin();
        i != waiting_set.end(); ++i) {
     BuilderRecord* waiting = *i;
     DCHECK(waiting->unresolved_deps().find(record) !=
            waiting->unresolved_deps().end());
@@ skipping 95 matching lines @@
   // Walk backwards since the dependency arrows point in the reverse direction.
   std::string ret;
   for (int i = static_cast<int>(cycle.size()) - 1; i >= 0; i--) {
     ret += "  " + cycle[i]->label().GetUserVisibleName(false);
     if (i != 0)
       ret += " ->\n";
   }
 
   return ret;
 }