Don't upgrade the severity of *everything* to an error in strong mode.

pkg/analyzer/test/source/error_processor_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.source.error_processor;
 
 import 'package:analyzer/source/analysis_options_provider.dart';
 import 'package:analyzer/source/error_processor.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 21 matching lines @@
   AnalysisError unused_local_variable = new AnalysisError(
       new TestSource(), 0, 1, HintCode.UNUSED_LOCAL_VARIABLE, [
     ['x']
   ]);
 
   AnalysisError use_of_void_result =
       new AnalysisError(new TestSource(), 0, 1, HintCode.USE_OF_VOID_RESULT, [
     ['x']
   ]);
 
+  AnalysisError non_bool_operand = new AnalysisError(
+      new TestSource(), 0, 1, StaticTypeWarningCode.NON_BOOL_OPERAND, [
+    ['x']
+  ]);
+
   oneTimeSetup();
 
   setUp(() {
     context = new TestContext();
   });
 
   group('ErrorProcessor', () {
     test('configureOptions', () {
       configureOptions('''
 analyzer:
   errors:
     invalid_assignment: error # severity ERROR
     missing_return: false # ignore
     unused_local_variable: true # skipped
     use_of_void_result: unsupported_action # skipped
 ''');
       expect(getProcessor(invalid_assignment).severity, ErrorSeverity.ERROR);
       expect(getProcessor(missing_return).severity, isNull);
       expect(getProcessor(unused_local_variable), isNull);
       expect(getProcessor(use_of_void_result), isNull);
     });
 
     test('upgrades static type warnings to errors in strong mode', () {
       configureOptions('''
 analyzer:
   strong-mode: true
 ''');
-      expect(getProcessor(invalid_assignment).severity, ErrorSeverity.ERROR);
+      expect(getProcessor(non_bool_operand).severity, ErrorSeverity.ERROR);
+    });
+
+    test('does not upgrade other warnings to errors in strong mode', () {
+      configureOptions('''
+analyzer:
+  strong-mode: true
+''');
+      expect(getProcessor(unused_local_variable), isNull);
     });
   });
 
   group('ErrorConfig', () {
     var config = '''
 analyzer:
   errors:
     invalid_assignment: unsupported_action # should be skipped
     missing_return: false
     unused_local_variable: error
@@ skipping 67 matching lines @@
 void oneTimeSetup() {
   List<Plugin> plugins = <Plugin>[];
   plugins.addAll(AnalysisEngine.instance.requiredPlugins);
   plugins.add(AnalysisEngine.instance.commandLinePlugin);
   plugins.add(AnalysisEngine.instance.optionsPlugin);
   ExtensionManager manager = new ExtensionManager();
   manager.processPlugins(plugins);
 }
 
 class TestContext extends AnalysisContextImpl {}