Add support for assert statements with messages to the analyzer.

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 65e391f5ec652faed36e1df01e57402d1ce9f200..b5ad0438a0a426db9a5d653082e3737bc6fa6b3a 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -2914,7 +2914,8 @@ class ParseDartTask extends SourceBasedAnalysisTask {
     Token tokenStream = getRequiredInput(TOKEN_STREAM_INPUT_NAME);
 
     RecordingErrorListener errorListener = new RecordingErrorListener();
-    Parser parser = new Parser(source, errorListener);
+    Parser parser = new Parser(source, errorListener,
+        enableAssertMessage: context.analysisOptions.enableAssertMessage);
     AnalysisOptions options = context.analysisOptions;
     parser.parseFunctionBodies = options.analyzeFunctionBodiesPredicate(source);
     parser.parseGenericMethods = options.enableGenericMethods;