Reduce the number of worker threads GN uses.

tools/gn/trace.cc

Index: tools/gn/trace.cc
diff --git a/tools/gn/trace.cc b/tools/gn/trace.cc
index c81079311486164f8d81c661f5bd1c0ed7665e12..4746310206f3e1200816313883b4e8e9f7e4de57 100644
--- a/tools/gn/trace.cc
+++ b/tools/gn/trace.cc
@@ -202,6 +202,7 @@ std::string SummarizeTraces() {
       case TraceItem::TRACE_FILE_LOAD:
       case TraceItem::TRACE_FILE_WRITE:
       case TraceItem::TRACE_DEFINE_TARGET:
+      case TraceItem::TRACE_ON_RESOLVED:
         break;  // Ignore these for the summary.
     }
   }
@@ -281,6 +282,9 @@ void SaveTraces(const base::FilePath& file_name) {
       case TraceItem::TRACE_DEFINE_TARGET:
         out << "\"define\"";
         break;
+      case TraceItem::TRACE_ON_RESOLVED:
+        out << "\"onresolved\"";
+        break;
       case TraceItem::TRACE_CHECK_HEADER:
         out << "\"hdr\"";
         break;