Fix an issue with duplicate reported analysis errors.

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 b68476b8b1a2c7d9d39d70c0612449e657d428dd..d46bc595f74e3ccbba25c0bcc1b72644811b3bf5 100644
--- a/pkg/analyzer_cli/lib/src/build_mode.dart
+++ b/pkg/analyzer_cli/lib/src/build_mode.dart
@@ -229,8 +229,8 @@ class BuildMode {
       for (Source source in explicitSources) {
         AnalysisErrorInfo errorInfo = context.getErrors(source);
         for (AnalysisError error in errorInfo.errors) {
-          ProcessedSeverity processedSeverity =
-              processError(error, options, context.analysisOptions);
+          ProcessedSeverity processedSeverity = determineProcessedSeverity(
+              error, options, context.analysisOptions);
           if (processedSeverity != null) {
             maxSeverity = maxSeverity.max(processedSeverity.severity);
           }
@@ -318,16 +318,14 @@ class BuildMode {
    */
   void _printErrors({String outputPath}) {
     StringBuffer buffer = new StringBuffer();
-    ErrorFormatter formatter = new ErrorFormatter(
-        buffer,
-        options,
-        stats,
-        (AnalysisError error) =>
-            processError(error, options, context.analysisOptions));
+    ErrorFormatter formatter = new HumanErrorFormatter(buffer, options, stats,
+        severityProcessor: (AnalysisError error) => determineProcessedSeverity(
+            error, options, context.analysisOptions));
     for (Source source in explicitSources) {
       AnalysisErrorInfo errorInfo = context.getErrors(source);
       formatter.formatErrors([errorInfo]);
     }
+    formatter.flush();
     if (!options.machineFormat) {
       stats.print(buffer);
     }