Support --persistent_worker flag in --build-mode.

pkg/analyzer_cli/lib/src/driver.dart

Index: pkg/analyzer_cli/lib/src/driver.dart
diff --git a/pkg/analyzer_cli/lib/src/driver.dart b/pkg/analyzer_cli/lib/src/driver.dart
index 070d06821fbfc2adee3da1eef04afe27dc1df162..f3016d56ba06af436d9433795b820e32d98233c1 100644
--- a/pkg/analyzer_cli/lib/src/driver.dart
+++ b/pkg/analyzer_cli/lib/src/driver.dart
@@ -244,7 +244,11 @@ class Driver implements CommandLineStarter {
   /// Perform analysis in build mode according to the given [options].
   ErrorSeverity _buildModeAnalyze(CommandLineOptions options) {
     return _analyzeAllTag.makeCurrentWhile(() {
-      return new BuildMode(options, stats).analyze();
+      if (options.buildModePersistentWorker) {
+        new WorkerLoop.std().run();
+      } else {
+        return new BuildMode(options, stats).analyze();
+      }
     });
   }