Add static type checking of "yield*" statements to analyzer.

tests/language/async_await_syntax_test.dart

 // Copyright (c) 2015, 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.
 
 // Test async/await syntax.
 
 import 'dart:async' show Stream;
 
 var yield = 0;
 var await = 0;
@@ skipping 150 matching lines @@
   var d01b = () async* => null; d01b();                        /// d01b: compile-time error
   var d01c = () sync* => null; d01c();                         /// d01c: compile-time error
   var d02a = () async {}; d02a();                              /// d02a: ok
   var d03a = () async* {}; d03a();                             /// d03a: ok
   var d04a = () sync* {}; d04a();                              /// d04a: ok
   var d04b = () sync {}; d04b();                               /// d04b: compile-time error
   var d05a = () async { await 0; }; d05a();                    /// d05a: ok
   var d06a = () async { await for (var o in st) {} }; d06a();  /// d06a: ok
   var d07a = () sync* { yield 0; }; d07a();                    /// d07a: ok
   var d08a = () sync* { yield* []; }; d08a();                  /// d08a: ok
-  var d08b = () sync* { yield*0+1; }; d08b();                  /// d08b: ok
+  var d08b = () sync* { yield*0+1; }; d08b();                  /// d08b: static type warning
   var d08c = () { yield*0+1; }; d08c();                        /// d08c: ok
   var d09a = () async* { yield 0; }; d09a();                   /// d09a: ok
-  var d10a = () async* { yield* []; }; d10a();                 /// d10a: ok
+  var d10a = () async* { yield* []; }; d10a();                 /// d10a: static type warning
 }
 
 
 void main() {
   var a;
   var c = new C();
   c = new C.e1(); /// e1: continued
   c = new C.e2(); /// e2: continued
   c = new C.e3(); /// e3: continued
   c = new C.e4(); /// e4: continued
@@ skipping 82 matching lines @@
   a = c.async;  /// b14c: continued
   a = c.async;  /// b14d: continued
   c.sync();     /// b15a: continued
   c.sync();     /// b15b: continued
   c.async();    /// b15c: continued
   c.async();    /// b15d: continued
 
   method1();
   method2();
 }