Add support for parsing, but not capturing, assers in constructor initializer lists

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index da8fcec03cc32cd827dbe223a38b59a3828a0837..9b2c997c4501692b9a8575583c638cabf193adb2 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -4123,6 +4123,7 @@ class ParseDartTask extends SourceBasedAnalysisTask {
     RecordingErrorListener errorListener = new RecordingErrorListener();
     Parser parser = new Parser(source, errorListener);
     AnalysisOptions options = context.analysisOptions;
+    parser.enableAssertInitializer = options.enableAssertInitializer;
     parser.parseAsync = options.enableAsync;
     parser.parseFunctionBodies = options.analyzeFunctionBodiesPredicate(source);
     parser.parseGenericMethods = options.enableGenericMethods;