Fix function subtyping crash

Fixes #588

BUG=
[email protected]

Review URL: https://codereview.chromium.org/2069653003 .

Author: leafpetersen

pkg/dev_compiler/lib/runtime/dart_sdk.js

@@ -1567,6 +1567,9 @@ dart_library.library('dart_sdk', null, /* Imports */[
     if (ft2 === core.Function) {
       return true;
     }
+    if (ft1 === core.Function) {
+      return false;
+    }
     let ret1 = ft1.returnType;
     let ret2 = ft2.returnType;
     let args1 = ft1.args;

pkg/dev_compiler/test/codegen/language/function_subtype_regression_ddc_588_test.dart

@@ -0,0 +1,14 @@
+import "package:expect/expect.dart";
+
+// regression test for ddc #588
+
+typedef int Int2Int(int x);
+
+void foo(List<Int2Int> list) {
+  list.forEach((f) => print(f(42)));
+}
+
+void main() {
+  var l = <Function>[];
+  Expect.throws(() => foo(l), (e) => e is TypeError);
+}

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart

@@ -496,6 +496,10 @@ isFunctionSubtype(ft1, ft2, covariant) => JS('', '''(() => {
     return true;
   }
 
+  if ($ft1 === $Function) {
+    return false;
+  }
+
   let ret1 = $ft1.returnType;
   let ret2 = $ft2.returnType;