Support generic methods in reflection.

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 07d1cbb60b64be5572297a6b6252656ed7ee68e3..3be1e9d4954b206bc79732c92d9c029a846b3cdf 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -679,11 +679,14 @@ class ReflectionInfo {
     if (JS('bool', 'typeof # == "number"', functionType)) {
       return getType(functionType);
     } else if (JS('bool', 'typeof # == "function"', functionType)) {
-      var fakeInstance = JS('', 'new #()', jsConstructor);
-      setRuntimeTypeInfo(
-          fakeInstance, JS('JSExtendableArray', '#["<>"]', fakeInstance));
-      return JS('=Object|Null', r'#.apply({$receiver:#})',
-                functionType, fakeInstance);
+      if (jsConstructor != null) {

[Siggi Cherem (dart-lang), 2017/01/03 18:58:13]

can you give me some extra details of when this happens? In particular, this
seems to handle more than just generics, or do we only expect functionType to be
a function if it has generic arguments?

[Johnni Winther, 2017/01/04 09:15:39]

It was provoked by lrn's landing of https://codereview.chromium.org/2529393002

This introduces function types the should not be substituted by the type
arguments of the current class which is what is now handled here. 

The change here corresponds to the change in js_helper.dart in
https://codereview.chromium.org/2565413002/

+        var fakeInstance = JS('', 'new #()', jsConstructor);
+        setRuntimeTypeInfo(
+            fakeInstance, JS('JSExtendableArray', '#["<>"]', fakeInstance));
+        return JS('=Object|Null', r'#.apply({$receiver:#})',
+                  functionType, fakeInstance);
+      }
+      return functionType;
     } else {
       throw new RuntimeError('Unexpected function type');
     }