cpsir unittests: move all unittests into individual files and test runners.

tests/compiler/dart2js/cps_ir/expected/interceptors_2.js

+// Expectation for test: 
+// main() {
+//   var l = ['hest', ['h', 'e', 's', 't']];
+//   print(l.length);
+//   for (int i  = 0; i < l.length; i++) {
+//     var x = l[i];
+//     for (int j = 0; j < x.length; j++) {
+//       print(x[j]);
+//     }
+//   }
+// }
+
+function() {
+  var l = ["hest", ["h", "e", "s", "t"]], i = 0, x, j;
+  for (P.print(2); i < 2; ++i) {
+    x = l[i];
+    for (j = 0; j < x.length; ++j)
+      P.print(x[j]);
+  }
+}