dart2js cps_ir: Seed type_propagation with constant bools from inference.

tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.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.dart';
 
@@ skipping 50 matching lines @@
     P.print(1);
     if (V.foo(false) === true)
       break;
   }
   P.print(2);
 }"""),
 const TestEntry("""
 foo(a) { print(a); return a; }
 
 main() {
+ foo(false);
  if (foo(true)) {
    print(1);
  } else {
    print(2);
  }
  print(3);
 }""", """
 function() {
+  V.foo(false);
   V.foo(true) ? P.print(1) : P.print(2);
   P.print(3);
 }"""),
 const TestEntry("""
 foo(a) { print(a); return a; }
 
 main() {
+ foo(false);
  if (foo(true)) {
    print(1);
    print(1);
  } else {
    print(2);
    print(2);
  }
  print(3);
 }""", """
 function() {
+  V.foo(false);
   if (V.foo(true)) {
     P.print(1);
     P.print(1);
   } else {
     P.print(2);
     P.print(2);
   }
   P.print(3);
 }"""),
 const TestEntry("""
@@ skipping 61 matching lines @@
     P.print(current1);
     if ($length !== xs.length)
       H.throwConcurrentModificationError(xs);
   }
 }"""),
 ];
 
 void main() {
   runTests(tests);
 }