Fix type checks and display for JS interop types.

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

Index: pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
index 4475a546052da9e2686174fc12db9158f1e385ac..61d99e9483db999172ef6bcc1ba521bc9d6ea610 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart
@@ -66,7 +66,7 @@ class Dynamic extends TypeRep {
   toString() => 'dynamic';
 }
 
-class LazyJSType implements Type {
+class LazyJSType extends TypeRep {
   final _jsTypeCallback;
   final _dartName;
 
@@ -114,7 +114,9 @@ _asInstanceOfLazyJSType(o, LazyJSType t) {
   return o;
 }
 
-bool _isJSObject(o) => JS('bool', '!dart.getReifiedType(o)[dart._runtimeType]');
+bool _isJSObject(o) =>
+    JS('bool', '!dart.getReifiedType(#)[dart._runtimeType]', o);
+bool _isJSType(t) => JS('bool', '!#[dart._runtimeType]', t);
 
 @JSExportName('dynamic')
 final _dynamic = new Dynamic();
@@ -577,12 +579,12 @@ getImplicitFunctionType(type) {
 bool isFunctionType(type) => JS('bool', '# instanceof # || # === #', type,
     AbstractFunctionType, type, Function);
 
-isLazyJSSubtype(LazyJSType t1, LazyJSType t2, isCovariant) {
-  if (t1 == t2) return true;
-
-  // All anonymous JS types are subtypes of each other.
-  if (t1._jsTypeCallback == null || t2._jsTypeCallback == null) return true;
-  return isClassSubType(t1._rawJSType, t2._rawJSType, isCovariant);
+isLazyJSSubtype(t1, LazyJSType t2, isCovariant) {
+  // All JS types are subtypes of anonymous JS types.
+  if (t2._jsTypeCallback == null) {
+    return _isJSType(t1);
+  }
+  return isClassSubType(t1, t2._rawJSType, isCovariant);

[vsm, 2017/03/31 15:14:08]

Depending on where you call this below, it may be safer to call _isSubtype -
e.g., there is no check that t1 is a class type.

[Jacob, 2017/04/01 00:51:13]

switched to _isSubtype. Agree that seems safer.

 }
 
 /// Returns true if [ft1] <: [ft2].
@@ -714,6 +716,10 @@ bool _isFutureOr(type) =>
 _isSubtype(t1, t2, isCovariant) => JS(
     '',
     '''(() => {
+  if ($t2 instanceof $LazyJSType) {

[vsm, 2017/03/31 15:14:08]

Can this be dropped to below the "trivial" checks?

Can this interact with FutureOr?  If so, it should probably be dropped below
that too.

[Jacob, 2017/04/01 00:51:13]

Moved down to right before t1 is forced to be a function subtype.

+    return $isLazyJSSubtype($t1, $t2, $isCovariant);
+  }
+
   if ($t1 === $t2) return true;
 
   // Trivially true.
@@ -775,11 +781,7 @@ _isSubtype(t1, t2, isCovariant) => JS(
   if ($isFunctionType($t1) && $isFunctionType($t2)) {
     return $isFunctionSubtype($t1, $t2, $isCovariant);
   }
-  
-  if ($t1 instanceof $LazyJSType && $t2 instanceof $LazyJSType) {
-    return $isLazyJSSubtype($t1, $t2, $isCovariant);
-  }
-  
+
   return false;
 })()''');