Analyzer CLI: fix machine format in build mode.

pkg/analyzer_cli/lib/src/build_mode.dart

Index: pkg/analyzer_cli/lib/src/build_mode.dart
diff --git a/pkg/analyzer_cli/lib/src/build_mode.dart b/pkg/analyzer_cli/lib/src/build_mode.dart
index cde1ab8661bbc76fed1428e0f26ebcea24823a8f..34e2c163761d897208a454692f0e24c41e0ddc18 100644
--- a/pkg/analyzer_cli/lib/src/build_mode.dart
+++ b/pkg/analyzer_cli/lib/src/build_mode.dart
@@ -368,9 +368,13 @@ class BuildMode {
    */
   void _printErrors({String outputPath}) {
     StringBuffer buffer = new StringBuffer();
-    ErrorFormatter formatter = new HumanErrorFormatter(buffer, options, stats,
-        severityProcessor: (AnalysisError error) => determineProcessedSeverity(
-            error, options, context.analysisOptions));
+    var severityProcessor = (AnalysisError error) =>
+        determineProcessedSeverity(error, options, context.analysisOptions);
+    ErrorFormatter formatter = options.machineFormat
+        ? new MachineErrorFormatter(buffer, options, stats,
+            severityProcessor: severityProcessor)
+        : new HumanErrorFormatter(buffer, options, stats,
+            severityProcessor: severityProcessor);
     for (Source source in explicitSources) {
       AnalysisErrorInfo errorInfo = context.getErrors(source);
       formatter.formatErrors([errorInfo]);