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

tests/compiler/dart2js/cps_ir/input/gvn_1.dart

+foo(x, list) {
+  var sum = 0;
+  for (int k = 0; k < 10; k++) {
+    // Everything can be hoisted out up to the index access which is
+    // blocked by the bounds check.
+    var a = x.left.left;
+    var b = x.left.right;
+    var c = x.right.left;
+    var d = x.right.right;
+    var i = a.value + c.value;
+    var j = b.value + d.value;
+    var z = list[i * j] + i;
+    sum += z;
+  }
+  return sum;
+}
+// Use a different class for each level in the tree, so type inference
+// is not confused.
+class Root {
+  Branch left, right;
+  Root(this.left, this.right);
+}
+class Branch {
+  Leaf left, right;
+  Branch(this.left, this.right);
+}
+class Leaf {
+  int value;
+  Leaf(this.value);
+}
+main() {
+  var x1 = new Leaf(1);
+  var x2 = new Leaf(10);
+  var x3 = new Leaf(20);
+  var x4 = new Leaf(-10);
+  var y1 = new Branch(x1, x2);
+  var y2 = new Branch(x3, x4);
+  var z  = new Root(y1, y2);
+  print(foo(z, [1,2,3,4,5,6,7,8,9,10]));
+}
+