Implement type inference for PropertySet.

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

Index: pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart.strong.expect b/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..448b85cbcfd87078f1236c1f3386197b46dc9134
--- /dev/null
+++ b/pkg/front_end/testcases/inference/downwards_inference_inside_top_level.dart.strong.expect
@@ -0,0 +1,19 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object {
+  field self::B<core::int> b = null;
+  constructor •() → void
+    : super core::Object::•()
+    ;
+}
+class B<T extends core::Object> extends core::Object {
+  constructor •(self::B::T x) → void
+    : super core::Object::•()
+    ;
+}
+static field self::A t1 = let final self::A #t1 = new self::A::•() in let final dynamic #t2 = #t1.{self::A::b} = new self::B::•<core::int>(1) in #t1;
+static field core::List<self::B<core::int>> t2 = <self::B<core::int>>[new self::B::•<core::int>(2)];
+static field core::List<self::B<dynamic>> t3 = <self::B<dynamic>>[new self::B::•<dynamic>(3)];
+static method main() → dynamic {}