cps-ir: Merge variables based on set-based liveness and graph coloring.

tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart

Index: tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
diff --git a/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart b/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
index e15bf3e99967ec5b977d5355f326efd27e556869..64515ce5d75c0f178abc058d35ca2b5d053ed5a3 100644
--- a/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
+++ b/tests/compiler/dart2js/js_backend_cps_ir_interceptors_test.dart
@@ -37,7 +37,7 @@ main() {
 }""",
 r"""
 function() {
-  var l, i, v0, x, j, v1;
+  var l, i, v0, x, j;
   l = ["hest", ["h", "e", "s", "t"]];
   P.print(J.getInterceptor$as(l).get$length(l));
   i = 0;
@@ -48,8 +48,8 @@ function() {
         x = J.getInterceptor$as(l).$index(l, i);
         j = 0;
         while (true) {
-          v1 = J.getInterceptor$as(x).get$length(x);
-          if (P.identical(J.getInterceptor$n(j).$lt(j, v1), true)) {
+          v0 = J.getInterceptor$as(x).get$length(x);
+          if (P.identical(J.getInterceptor$n(j).$lt(j, v0), true)) {
             P.print(J.getInterceptor$as(x).$index(x, j));
             j = J.getInterceptor$ns(j).$add(j, 1);
           } else {