Issue 19929. Record the propagated type into LHS of the assignment.

pkg/analyzer/test/generated/resolver_test.dart

 // Copyright (c) 2014, 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 engine.resolver_test;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 12742 matching lines @@
     SimpleIdentifier identifier = statement.expression as SimpleIdentifier;
     InterfaceType propagatedType = identifier.propagatedType as InterfaceType;
     expect(propagatedType.element, same(typeProvider.mapType.element));
     List<DartType> typeArguments = propagatedType.typeArguments;
     expect(typeArguments, hasLength(2));
     expect(typeArguments[0], same(typeProvider.dynamicType));
     expect(typeArguments[1], same(typeProvider.dynamicType));
   }
 
   void test_mergePropagatedTypes_afterIfThen_different() {
-    _assertTypeOfMarkedExpression(r'''
+    String code = r'''
 main() {
   var v = 0;
   if (v != null) {
     v = '';
   }
-  return v; // marker
-}''', null, null);
+  return v;
+}''';
+    {
+      SimpleIdentifier identifier = _findMarkedIdentifier(code, "v;");
+      expect(identifier.propagatedType, null);
+    }
+    {
+      SimpleIdentifier identifier = _findMarkedIdentifier(code, "v = '';");
+      expect(identifier.propagatedType, typeProvider.stringType);
+    }
   }
 
   void test_mergePropagatedTypes_afterIfThen_same() {
     _assertTypeOfMarkedExpression(r'''
 main() {
   var v = 1;
   if (v != null) {
     v = 2;
   }
   return v; // marker
@@ skipping 963 matching lines @@
         // check propagated type
         FunctionType propagatedType = node.propagatedType as FunctionType;
         expect(propagatedType.returnType, test.typeProvider.stringType);
       } on AnalysisException catch (e, stackTrace) {
         thrownException[0] = new CaughtException(e, stackTrace);
       }
     }
     return null;
   }
 }