Chase imports in analyzer's front_end_inference_test.

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

+library test;
+import self as self;
+import "./infer_from_variables_in_non_cycle_imports_with_flag_a.dart" as inf;
+import "dart:core" as core;
+
+static field core::int y = inf::x;
+static method test1() → dynamic {
+  inf::x = "hi";
+  self::y = "hi";
+}
+static method main() → dynamic {}