Add type inference for while and do loops.

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

Index: pkg/front_end/testcases/inference_new/while_loop.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference_new/while_loop.dart.strong.expect b/pkg/front_end/testcases/inference_new/while_loop.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..411b4440d81530321325f57abf005ec3a5580387
--- /dev/null
+++ b/pkg/front_end/testcases/inference_new/while_loop.dart.strong.expect
@@ -0,0 +1,12 @@
+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 {
+  while (self::f<core::bool>()) {
+    core::int x = 0;
+  }
+}
+static method main() → dynamic {}