Implement type inference for null-aware property gets.

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

Index: pkg/front_end/testcases/inference/null_aware_property_get.dart.direct.expect
diff --git a/pkg/front_end/testcases/inference/null_aware_property_get.dart.direct.expect b/pkg/front_end/testcases/inference/null_aware_property_get.dart.direct.expect
new file mode 100644
index 0000000000000000000000000000000000000000..375ea203595117e534c1769443b187ca22b5adde
--- /dev/null
+++ b/pkg/front_end/testcases/inference/null_aware_property_get.dart.direct.expect
@@ -0,0 +1,14 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+class C extends core::Object {
+  field core::int x = null;
+  constructor •() → void
+    : super core::Object::•()
+    ;
+}
+static method f(self::C c) → void {
+  dynamic x = let final dynamic #t1 = c in #t1.==(null) ? null : #t1.x;
+}
+static method main() → dynamic {}