Implement type inference for "not" expressions.

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

Index: pkg/front_end/testcases/inference/infer_prefix_expression.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/infer_prefix_expression.dart.strong.expect b/pkg/front_end/testcases/inference/infer_prefix_expression.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..6137c7c9bcd210a56104215703d01bc6363ac835
--- /dev/null
+++ b/pkg/front_end/testcases/inference/infer_prefix_expression.dart.strong.expect
@@ -0,0 +1,12 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+static field core::bool a_not = !true;
+static field core::int a_complement = 1.{core::int::~}();
+static field core::int a_negate = 1.{core::int::unary-}();
+static method main() → dynamic {
+  self::a_not;
+  self::a_complement;
+  self::a_negate;
+}