Address late comments from CL 50313007.

dart/sdk/lib/_internal/lib/js_mirrors.dart

Index: dart/sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/dart/sdk/lib/_internal/lib/js_mirrors.dart b/dart/sdk/lib/_internal/lib/js_mirrors.dart
index ba809de98874a716724c141d3153732464e8504d..cb4897515bf99a2eaedaacf7ac7245b686bb4ace 100644
--- a/dart/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/dart/sdk/lib/_internal/lib/js_mirrors.dart
@@ -1631,7 +1631,10 @@ class JsClosureMirror extends JsInstanceMirror implements ClosureMirror {
   MethodMirror get function {
     String cacheName = Primitives.mirrorFunctionCacheName;
     JsMethodMirror cachedFunction;
-    // TODO(ahe): Restore caching.
+    // TODO(ahe): Restore caching. We used to have a one-to-one correspondence
+    // between a method that could be torn off and a constructor (the bound
+    // closure classes). But now all tear-offs share the same constructor (a
+    // class called BoundClosure in js_helper.dart).
     //= JS('JsMethodMirror|Null', r'#.constructor[#]', reflectee, cacheName);
     if (cachedFunction != null) return cachedFunction;
     disableTreeShaking();
@@ -1769,6 +1772,7 @@ class JsMethodMirror extends JsDeclarationMirror implements MethodMirror {
         var functionType = info.functionType;
         var type;
         if (functionType is int) {
+          // A reference to a type variable in init.metadata.
           type = new JsFunctionTypeMirror(info.computeFunctionRti(null), this);
           assert(_parameterCount == type.parameters.length);
         } else if (isTopLevel) {