Record static types in the desugaring of null-aware property gets.

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

Index: pkg/front_end/testcases/inference/null_aware_property_get.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/null_aware_property_get.dart.strong.expect b/pkg/front_end/testcases/inference/null_aware_property_get.dart.strong.expect
index 0665447195e59c6a8e0996faa5e2849faa8ab213..48478c83fab5c40685d5543e1cd1d1a57acefbff 100644
--- a/pkg/front_end/testcases/inference/null_aware_property_get.dart.strong.expect
+++ b/pkg/front_end/testcases/inference/null_aware_property_get.dart.strong.expect
@@ -9,6 +9,6 @@ class C extends core::Object {
     ;
 }
 static method f(self::C c) → void {
-  core::int x = let final dynamic #t1 = c in #t1.==(null) ?{dynamic} null : #t1.{self::C::x};
+  core::int x = let final self::C #t1 = c in #t1.==(null) ?{core::int} null : #t1.{self::C::x};
 }
 static method main() → dynamic {}