Make the exit code for dartanalyzer more deterministic.

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 08667cade2e0acf2cba0a05c028b84562db99253..cde1ab8661bbc76fed1428e0f26ebcea24823a8f 100644
--- a/pkg/analyzer_cli/lib/src/build_mode.dart
+++ b/pkg/analyzer_cli/lib/src/build_mode.dart
@@ -249,10 +249,10 @@ class BuildMode {
       for (Source source in explicitSources) {
         AnalysisErrorInfo errorInfo = context.getErrors(source);
         for (AnalysisError error in errorInfo.errors) {
-          ProcessedSeverity processedSeverity = determineProcessedSeverity(
+          ErrorSeverity processedSeverity = determineProcessedSeverity(
               error, options, context.analysisOptions);
           if (processedSeverity != null) {
-            maxSeverity = maxSeverity.max(processedSeverity.severity);
+            maxSeverity = maxSeverity.max(processedSeverity);
           }
         }
       }