Handle assert with message in type inference

pkg/compiler/lib/src/inferrer/inferrer_visitor.dart

 // Copyright (c) 2013, 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 inferrer_visitor;
 
 import 'dart:collection' show IterableMixin;
 
 import '../common.dart';
 import '../compiler.dart' show Compiler;
@@ skipping 745 matching lines @@
 
   @override
   T apply(Node node, _) => visit(node);
 
   T handleSendSet(SendSet node);
 
   T handleDynamicInvoke(Send node);
 
   T visitAssert(Assert node) {
     // Avoid pollution from assert statement unless enabled.
-    if (compiler.options.enableUserAssertions) {
-      super.visitAssert(node);
+    if (!compiler.options.enableUserAssertions) {
+      return null;
     }
+    List<Send> tests = <Send>[];
+    bool simpleCondition = handleCondition(node.condition, tests);
+    LocalsHandler<T> saved = locals;
+    locals = new LocalsHandler<T>.from(locals, node);
+    updateIsChecks(tests, usePositive: true);
+
+    LocalsHandler<T> thenLocals = locals;
+    locals = new LocalsHandler<T>.from(saved, node);
+    if (simpleCondition) updateIsChecks(tests, usePositive: false);
+    visit(node.message);
+    locals.seenReturnOrThrow = true;
+    saved.mergeDiamondFlow(thenLocals, locals);
+    locals = saved;
     return null;
   }
 
   T visitAsyncForIn(AsyncForIn node);
 
   T visitSyncForIn(SyncForIn node);
 
   T visitReturn(Return node);
 
   T visitFunctionExpression(FunctionExpression node);
@@ skipping 698 matching lines @@
     return type;
   }
 
   T visitCascade(Cascade node) {
     // Ignore the result of the cascade send and return the type of the cascade
     // receiver.
     visit(node.expression);
     return cascadeReceiverStack.removeLast();
   }
 }