fix #25220, infer generic type from constructor arguments

pkg/analyzer/test/generated/strong_mode_test.dart

 // Copyright (c) 2016, 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 analyzer.test.generated.strong_mode_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
@@ skipping 780 matching lines @@
         A<int, String> a2 = new D<int, String>("hello");
         A<int, String> a3 = new D<String, String>.named("hello");
         A<int, String> a4 = new D<num, dynamic>("hello");
         A<int, String> a5 = new D<dynamic, dynamic>.named("hello");
       }
       void test7() {
         A<int, String> a0 = new D(3);
         A<int, String> a1 = new D.named(3);
       }
       void test8() {
-        // Currently we only allow variable constraints.  Test that we reject.
         A<C<int>, String> a0 = new E("hello");
       }
       void test9() { // Check named and optional arguments
         A<int, String> a0 = new F(3, "hello", a: [3], b: ["hello"]);
         A<int, String> a1 = new F(3, "hello", a: ["hello"], b:[3]);
         A<int, String> a2 = new F.named(3, "hello", 3, "hello");
         A<int, String> a3 = new F.named(3, "hello");
         A<int, String> a4 = new F.named(3, "hello", "hello", 3);
         A<int, String> a5 = new F.named(3, "hello", "hello");
       }
@@ skipping 102 matching lines @@
     {
       List<Statement> statements =
           AstFinder.getStatementsInTopLevelFunction(unit, "test7");
       hasType(assertDOf([_isDynamic, _isString]), rhs(statements[0]));
       hasType(assertDOf([_isDynamic, _isString]), rhs(statements[1]));
     }
 
     {
       List<Statement> statements =
           AstFinder.getStatementsInTopLevelFunction(unit, "test8");
-      hasType(assertEOf([_isDynamic, _isDynamic]), rhs(statements[0]));
+      hasType(assertEOf([_isInt, _isString]), rhs(statements[0]));
     }
 
     {
       List<Statement> statements =
           AstFinder.getStatementsInTopLevelFunction(unit, "test9");
       hasType(assertFOf([_isInt, _isString]), rhs(statements[0]));
       hasType(assertFOf([_isInt, _isString]), rhs(statements[1]));
       hasType(assertFOf([_isInt, _isString]), rhs(statements[2]));
       hasType(assertFOf([_isInt, _isString]), rhs(statements[3]));
       hasType(assertFOf([_isInt, _isString]), rhs(statements[4]));
@@ skipping 1373 matching lines @@
 main() {
   var v = x;
   v; // marker
 }
 int x = 3;
 ''';
     assertPropagatedAssignedType(code, typeProvider.intType, null);
     assertTypeOfMarkedExpression(code, typeProvider.intType, null);
   }
 }