Allow yield expressions without a RHS.

test/mjsunit/harmony/generators-iteration.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 319 matching lines @@
         throw (yield (1 + (yield 2) + 3))
       } catch (e) {
         if (typeof e == 'object') throw e;
         return e + (yield (4 + (yield 5) + 6));
       }
     },
     [2, NaN, 5, NaN, NaN],
     "foo",
     [2, "1foo3", 5, "4foo6", "foofoo"]);
 
+// Yield with no arguments yields undefined.
+TestGenerator(
+    function* g26() { return yield yield },
+    [undefined, undefined, undefined],
+    "foo",
+    [undefined, "foo", "foo"]);
+
+// A newline causes the parser to stop looking for an argument to yield.
+TestGenerator(
+    function* g27() {
+      yield
+      3
+      return
+    },
+    [undefined, undefined],
+    "foo",
+    [undefined, undefined]);
+
 // Generator function instances.
 TestGenerator(GeneratorFunction(),
               [undefined],
               "foo",
               [undefined]);
 
 TestGenerator(new GeneratorFunction(),
               [undefined],
               "foo",
               [undefined]);
@@ skipping 291 matching lines @@
   function TestThrowRecursion() {
     function* g() { yield iter.throw(1); }
     var iter = g();
     return iter.next();
   }
   assertThrows(TestNextRecursion, Error);
   assertThrows(TestSendRecursion, Error);
   assertThrows(TestThrowRecursion, Error);
 }
 TestRecursion();