Add type inference for while and do loops.

pkg/front_end/testcases/inference_new/do_loop.dart.strong.expect

Index: pkg/front_end/testcases/inference_new/do_loop.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference_new/do_loop.dart.strong.expect b/pkg/front_end/testcases/inference_new/do_loop.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..9262769c972dbc66ac0d0399330c25a765df37dd
--- /dev/null
+++ b/pkg/front_end/testcases/inference_new/do_loop.dart.strong.expect
@@ -0,0 +1,13 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+static method f<T extends core::Object>() → self::f::T
+  return null;
+static method test() → void {
+  do {
+    core::int x = 0;
+  }
+  while (self::f<core::bool>())
+}
+static method main() → dynamic {}