Add support for assert statements with messages to the analyzer.

pkg/analyzer/lib/src/generated/testing/ast_factory.dart

Index: pkg/analyzer/lib/src/generated/testing/ast_factory.dart
diff --git a/pkg/analyzer/lib/src/generated/testing/ast_factory.dart b/pkg/analyzer/lib/src/generated/testing/ast_factory.dart
index bb758b3533f72dcd7bf850f6430e114dc7ad8e7e..ab9a75cc1a6e452e1d74f92ca338d49d2f0c77c3 100644
--- a/pkg/analyzer/lib/src/generated/testing/ast_factory.dart
+++ b/pkg/analyzer/lib/src/generated/testing/ast_factory.dart
@@ -46,11 +46,14 @@ class AstFactory {
       new AsExpression(
           expression, TokenFactory.tokenFromKeyword(Keyword.AS), type);
 
-  static AssertStatement assertStatement(Expression condition) =>
+  static AssertStatement assertStatement(Expression condition,
+          [Expression message]) =>
       new AssertStatement(
           TokenFactory.tokenFromKeyword(Keyword.ASSERT),
           TokenFactory.tokenFromType(TokenType.OPEN_PAREN),
           condition,
+          message == null ? null : TokenFactory.tokenFromType(TokenType.COMMA),
+          message,
           TokenFactory.tokenFromType(TokenType.CLOSE_PAREN),
           TokenFactory.tokenFromType(TokenType.SEMICOLON));