Implement 'analysis.getErrors' for the new driver.

pkg/analyzer/test/src/task/strong/strong_test_helper.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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 library analyzer.test.src.task.strong.strong_test_helper;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
@@ skipping 157 matching lines @@
   final prefix = 'STRONG_MODE_';
   if (name.startsWith(prefix)) {
     return name.substring(prefix.length);
   } else {
     return name;
   }
 }
 
 ErrorSeverity _errorSeverity(AnalysisContext context, AnalysisError error) {
   // Attempt to process severity in a similar way to analyzer_cli and server.
-  return ErrorProcessor.getProcessor(context, error)?.severity ??
+  return ErrorProcessor
+          .getProcessor(context.analysisOptions, error)
+          ?.severity ??
       error.errorCode.errorSeverity;
 }
 
 void _expectErrors(AnalysisContext context, CompilationUnit unit,
     List<AnalysisError> actualErrors) {
   var expectedErrors = _findExpectedErrors(unit.beginToken);
 
   // Sort both lists: by offset, then level, then name.
   actualErrors.sort((x, y) {
     int delta = x.offset.compareTo(y.offset);
@@ skipping 217 matching lines @@
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (uri.scheme == 'package') {
       return (provider.getResource(
               provider.convertPath('/packages/' + uri.path)) as File)
           .createSource(uri);
     }
     return super.resolveAbsolute(uri, actualUri);
   }
 }