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

tests/compiler/dart2js/cps_ir/input/interceptors_2.dart

Index: tests/compiler/dart2js/cps_ir/input/interceptors_2.dart
diff --git a/tests/compiler/dart2js/cps_ir/input/interceptors_2.dart b/tests/compiler/dart2js/cps_ir/input/interceptors_2.dart
new file mode 100644
index 0000000000000000000000000000000000000000..785348605bbd08137317b2ce70041a9d11a9b42c
--- /dev/null
+++ b/tests/compiler/dart2js/cps_ir/input/interceptors_2.dart
@@ -0,0 +1,10 @@
+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]);
+    }
+  }
+}