Fix handling of lazy and and or in async functions.

tests/compiler/dart2js/async_await_js_transform_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.
 
 import "package:expect/expect.dart";
 import "package:compiler/src/js/js.dart";
 import "package:compiler/src/js/rewrite_async.dart";
 
 import "backend_dart/dart_printer_test.dart" show PrintDiagnosticListener;
 
@@ skipping 244 matching lines @@
   function __body(__errorCode, __result) {
     if (__errorCode === 1) {
       __currentError = __result;
       __goto = __handler;
     }
     while (true)
       switch (__goto) {
         case 0:
           // Function start
           __temp1 = foo1();
-          if (__temp1) {
+          if (__temp1)
+            __result = __temp1;
+          else {
             // goto then
             __goto = 2;
             break;
-          } else
-            __result = __temp1;
+          }
           // goto join
           __goto = 3;
           break;
         case 2:
           // then
           __goto = 4;
           return thenHelper(foo2(), __body, __completer);
         case 4:
           // returning from await.
         case 3:
           // join
           a = __result;
           __goto = 5;
           return thenHelper(foo1(), __body, __completer);
         case 5:
           // returning from await.
           b = __result || foo2();
           __goto = 8;
           return thenHelper(foo1(), __body, __completer);
         case 8:
           // returning from await.
           __temp1 = __result;
-          if (__temp1) {
+          if (__temp1)
+            __result = __temp1;
+          else {
             // goto then
             __goto = 6;
             break;
-          } else
-            __result = __temp1;
+          }
           // goto join
           __goto = 7;
           break;
         case 6:
           // then
           __temp1 = foo3;
           __goto = 9;
           return thenHelper(foo2(), __body, __completer);
         case 9:
           // returning from await.
           __result = __temp1(__result);
         case 7:
           // join
           c = __result;
           d = foo1() || foo2();
           __temp1 = foo1();
-          if (__temp1)
-            __result = __temp1;
-          else {
+          if (__temp1) {
             // goto then
             __goto = 10;
             break;
-          }
+          } else
+            __result = __temp1;
           // goto join
           __goto = 11;
           break;
         case 10:
           // then
           __goto = 12;
           return thenHelper(foo2(), __body, __completer);
         case 12:
           // returning from await.
         case 11:
           // join
           e = __result;
           __goto = 13;
           return thenHelper(foo1(), __body, __completer);
         case 13:
           // returning from await.
           f = __result && foo2();
           __goto = 16;
           return thenHelper(foo1(), __body, __completer);
         case 16:
           // returning from await.
           __temp1 = __result;
-          if (__temp1)
-            __result = __temp1;
-          else {
+          if (__temp1) {
             // goto then
             __goto = 14;
             break;
-          }
+          } else
+            __result = __temp1;
           // goto join
           __goto = 15;
           break;
         case 14:
           // then
           __goto = 17;
           return thenHelper(foo2(), __body, __completer);
         case 17:
           // returning from await.
         case 15:
@@ skipping 696 matching lines @@
           // implicit return
           return thenHelper(null, 0, __completer, null);
         case 1:
           // rethrow
           return thenHelper(__currentError, 1, __completer);
       }
   }
   return thenHelper(null, __body, __completer, null);
 }""");
 }