Implement type inference for "not" expressions.

pkg/front_end/testcases/inference/infer_prefix_expression.dart

Index: pkg/front_end/testcases/inference/infer_prefix_expression.dart
diff --git a/pkg/front_end/testcases/inference/infer_prefix_expression.dart b/pkg/front_end/testcases/inference/infer_prefix_expression.dart
index 8a028116c8b091433b4626c7e37d1b97c72ebca6..ea88fe0a50a24d902c01fff97734ac5ce7c03fc6 100644
--- a/pkg/front_end/testcases/inference/infer_prefix_expression.dart
+++ b/pkg/front_end/testcases/inference/infer_prefix_expression.dart
@@ -8,3 +8,9 @@ library test;
 var /*@topType=bool*/ a_not = !true;
 var /*@topType=int*/ a_complement = /*@target=int::~*/ ~1;
 var /*@topType=int*/ a_negate = /*@target=int::unary-*/ -1;
+
+main() {
+  a_not;
+  a_complement;
+  a_negate;
+}