Add hooks for changing priorities of warnings to errors in strong mode

pkg/analyzer_cli/lib/src/analyzer_impl.dart

Index: pkg/analyzer_cli/lib/src/analyzer_impl.dart
diff --git a/pkg/analyzer_cli/lib/src/analyzer_impl.dart b/pkg/analyzer_cli/lib/src/analyzer_impl.dart
index 428869ff2400d1fe821568db6a13e1ec4c9e57d5..e6f13707d40170bec535ed57c8c5e1cfd4f4a5f3 100644
--- a/pkg/analyzer_cli/lib/src/analyzer_impl.dart
+++ b/pkg/analyzer_cli/lib/src/analyzer_impl.dart
@@ -254,27 +254,28 @@ class AnalyzerImpl {
   static ErrorSeverity computeSeverity(
       AnalysisError error, CommandLineOptions options,
       [AnalysisContext context]) {
+    bool isStrongMode = false;
     if (context != null) {
       ErrorProcessor processor = ErrorProcessor.getProcessor(context, error);
       // If there is a processor for this error, defer to it.
       if (processor != null) {
         return processor.severity;
       }
+      isStrongMode = context.analysisOptions.strongMode;
     }
 
     if (!options.enableTypeChecks &&
         error.errorCode.type == ErrorType.CHECKED_MODE_COMPILE_TIME_ERROR) {
       return ErrorSeverity.INFO;
-    }
-
-    if (options.hintsAreFatal && error.errorCode is HintCode) {
+    } else if (options.hintsAreFatal && error.errorCode is HintCode) {
       return ErrorSeverity.ERROR;
-    }
-
-    if (options.lintsAreFatal && error.errorCode is LintCode) {
+    } else if (options.lintsAreFatal && error.errorCode is LintCode) {
+      return ErrorSeverity.ERROR;
+    } else if (isStrongMode &&
+        error is StaticWarningCode &&
+        (error as StaticWarningCode).isStrongModeError) {
       return ErrorSeverity.ERROR;
     }
-
     return error.errorCode.errorSeverity;
   }