set exitCode on errors or warnings

pkg/analyzer/bin/analyzer.dart

Index: pkg/analyzer/bin/analyzer.dart
diff --git a/pkg/analyzer/bin/analyzer.dart b/pkg/analyzer/bin/analyzer.dart
index a9333c051ebc5758b8c09283bc1baed99b60b7c6..bab77b6fa4cbd1c82965230ad18006d7bdc60d18 100644
--- a/pkg/analyzer/bin/analyzer.dart
+++ b/pkg/analyzer/bin/analyzer.dart
@@ -70,7 +70,14 @@ _runAnalyzer(CommandLineOptions options, [bool async = true]) {
   if (async) {
     return analyzer.analyzeAsync();
   } else {
-    return analyzer.analyzeSync();
+    var errorSeverity = analyzer.analyzeSync();
+    if (errorSeverity == ErrorSeverity.ERROR) {
+      exitCode = errorSeverity.ordinal;
+    }
+    if (options.warningsAreFatal && errorSeverity == ErrorSeverity.WARNING) {
+      exitCode = errorSeverity.ordinal;
+    }
+    return errorSeverity;
   }
 }