Implement type inference of method invocations in Fasta.

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

Index: pkg/front_end/testcases/inference/inferred_type_custom_index_op_via_interface.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/inferred_type_custom_index_op_via_interface.dart.strong.expect b/pkg/front_end/testcases/inference/inferred_type_custom_index_op_via_interface.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..77016febd363e0cd0518ec36564e4eae6fe965ef
--- /dev/null
+++ b/pkg/front_end/testcases/inference/inferred_type_custom_index_op_via_interface.dart.strong.expect
@@ -0,0 +1,21 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+class I extends core::Object {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  operator [](core::int index) → core::bool
+    return true;
+}
+abstract class C extends core::Object implements self::I {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+}
+static method f() → dynamic {
+  self::C c;
+  core::bool x = c.[](0);
+}
+static method main() → dynamic {}