Improve optimization of operations on indexables by using more inferred type information and by dis…

tests/compiler/dart2js/simple_inferrer_relations_test.dart

 // Copyright (c) 2013, 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
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
@@ skipping 22 matching lines @@
 class B extends A {
   B(int foo, this.bar) : super(foo);
   int bar;
   operator==(other) {
     if (other.bar != bar) return false;
     return other.foo == foo;
   }
 }
 
 main() {
-  var both = [new A(inscrutable(0) == 0 ? 42 : "fish"),
-              new B(0, inscrutable(0) == 0 ? 2 : "horse")];
-  if (both[1] == both[0]) {
+  var a = new A(inscrutable(0) == 0 ? 42 : "fish");
+  var b = new B(0, inscrutable(0) == 0 ? 2 : "horse");
+  var c = inscrutable(0) == 0 ? a : "kurt";
+  var d = inscrutable(0) == 0 ? b : "gert";
+  if (c == d) {
     print("hestfisk");
   }
 }
 """;
 
 void main() {
   String generated = compileAll(TEST);
-  if (!generated.contains(r'if ($.$eq(both[1], both[0]))')) {
+  if (!generated.contains(r'if ($.$eq(c, d))')) {
     print(generated);
     Expect.fail("missing elision of '=== true'");
   }
 }