Add GN buildfile for gfx

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 233 matching lines @@
 }
 
 BuilderRecord* Builder::GetOrCreateRecordOfType(const Label& label,
                                                 const ParseNode* request_from,
                                                 BuilderRecord::ItemType type,
                                                 Err* err) {
   BuilderRecord* record = GetRecord(label);
   if (!record) {
     // Not seen this record yet, create a new one.
     record = new BuilderRecord(type, label);
+    record->set_originally_referenced_from(request_from);
     records_[label] = record;
     return record;
   }
 
   // Check types.
   if (record->type() != type) {
     *err = Err(request_from, "Item type does not match.",
         "The item \"" + label.GetUserVisibleName(false) +
-        "\" was expected\nto be a " +
+        "\"\nwas expected to be a " +
         BuilderRecord::GetNameForType(type) +
-        " but was previously\n referenced as a " +
+        " but was previously referenced as a " +
         BuilderRecord::GetNameForType(record->type()));
-    err->AppendSubErr(Err(record->originally_referenced_from(),
-                          "The previous reference was here."));
+    if (record->originally_referenced_from()) {
+      err->AppendSubErr(Err(record->originally_referenced_from(),
+                            "The previous reference was here."));
+    }
     return NULL;
   }
 
   return record;
 }
 
 BuilderRecord* Builder::GetResolvedRecordOfType(const Label& label,
                                                 const ParseNode* origin,
                                                 BuilderRecord::ItemType type,
                                                 Err* err) {
@@ skipping 184 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;
 }