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

tests/compiler/dart2js/cps_ir/expected/control_flow_3.js

+// Expectation for test: 
+// foo(a) { print(a); return a; }
+// 
+// main() {
+//   for (int i = 0; foo(true); i = foo(i)) {
+//     print(1);
+//     if (foo(false)) break;
+//   }
+//   print(2);
+// }
+
+function() {
+  while (true) {
+    P.print(true);
+    if (true === true) {
+      P.print(1);
+      P.print(false);
+      if (false !== true) {
+        P.print(0);
+        continue;
+      }
+    }
+    P.print(2);
+    return null;
+  }
+}