Minor type inference fixes to do with null and bottom types.

pkg/front_end/testcases/inference/infer_throw.dart.strong.expect

Index: pkg/front_end/testcases/inference/infer_throw.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/infer_throw.dart.strong.expect b/pkg/front_end/testcases/inference/infer_throw.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..35ee7d79fdf712158eed861604019a17e0c96f72
--- /dev/null
+++ b/pkg/front_end/testcases/inference/infer_throw.dart.strong.expect
@@ -0,0 +1,10 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+static field core::bool t = true;
+static field dynamic a = throw 0;
+static field core::int b = (throw 0) ? 1 : 2;
+static field core::int c = self::t ? throw 1 : 2;
+static field core::int d = self::t ? 1 : throw 2;
+static method main() → dynamic {}