Add CPS IR transformation to make the JavaScript backend specific semantics explicit in the tree.

tests/compiler/dart2js/js_backend_cps_ir_control_flow.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.
 
 // Tests of control flow statements.
 
 library control_flow_tests;
 
 import 'js_backend_cps_ir_test.dart';
 
 const List<TestEntry> tests = const [
   const TestEntry("""
 main() {
   while (true);
 }
 """, """
 function() {
-  while (true)
+  while (P.identical(true, true))
     ;
+  return null;
 }"""),
   const TestEntry("""
 foo(a) => a;
 
 main() {
   while (true) {
     l: while (true) {
       while (foo(true)) {
         if (foo(false)) break l;
       }
       print(1);
     }
     print(2);
   }
 }
 """, """
 function() {
-  L0:
-    while (true)
-      while (true) {
-        while (P.identical(V.foo(true), true))
-          if (P.identical(V.foo(false), true)) {
-            P.print(2);
-            continue L0;
-          }
-        P.print(1);
-      }
+  L2:
+    while (P.identical(true, true))
+      L1:
+        while (true) {
+          L0:
+            if (P.identical(true, true)) {
+              while (P.identical(V.foo(true), true))
+                if (!P.identical(V.foo(false), true))
+                  ;
+                else
+                  break L0;
+              P.print(1);
+              continue L1;
+            }
+          P.print(2);
+          continue L2;
+        }
+  return null;
 }"""),
   const TestEntry("""
 foo(a) => a;
 
 main() {
   for (int i = 0; foo(true); i = foo(i)) {
     print(1);
     if (foo(false)) break;
   }
   print(2);
 }""", """
 function() {
   var i;
   i = 0;
-  L1:
+  L3:
     while (true) {
       if (P.identical(V.foo(true), true)) {
         P.print(1);
         if (!P.identical(V.foo(false), true)) {
           i = V.foo(i);
-          continue L1;
+          continue L3;
         }
       }
       P.print(2);
       return null;
     }
 }"""),
 const TestEntry("""
 foo(a) => a;
 
 main() {
@@ skipping 27 matching lines @@
     P.print(1);
     P.print(1);
   } else {
     P.print(2);
     P.print(2);
   }
   P.print(3);
   return null;
 }"""),
 ];