Support user generated custom native JS classes.

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index ce801a9b8414fb83ec11b204a952f63a9ed69dcb..c5c7eb0b6eb1e14ba287c8420e04d113992feb11 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -289,6 +289,7 @@ class JavaScriptBackend extends Backend {
   ClassElement jsBoolClass;
   ClassElement jsPlainJavaScriptObjectClass;
   ClassElement jsUnknownJavaScriptObjectClass;
+  ClassElement jsJavaScriptFunctionClass;
 
   ClassElement jsIndexableClass;
   ClassElement jsMutableIndexableClass;
@@ -1039,6 +1040,7 @@ class JavaScriptBackend extends Backend {
         enqueue(enqueuer, getNativeInterceptorMethod, registry);
         enqueueClass(enqueuer, jsInterceptorClass, compiler.globalDependencies);
         enqueueClass(enqueuer, jsPlainJavaScriptObjectClass, registry);
+        enqueueClass(enqueuer, jsJavaScriptFunctionClass, registry);
       } else if (cls == mapLiteralClass) {
         // For map literals, the dependency between the implementation class
         // and [Map] is not visible, so we have to add it manually.
@@ -1119,6 +1121,8 @@ class JavaScriptBackend extends Backend {
       addInterceptors(jsPlainJavaScriptObjectClass, enqueuer, registry);
     } else if (cls == jsUnknownJavaScriptObjectClass) {
       addInterceptors(jsUnknownJavaScriptObjectClass, enqueuer, registry);
+    } else if (cls == jsJavaScriptFunctionClass) {
+      addInterceptors(jsJavaScriptFunctionClass, enqueuer, registry);
     } else if (Elements.isNativeOrExtendsNative(cls)) {
       addInterceptorsForNativeClassMembers(cls, enqueuer);
     } else if (cls == jsIndexingBehaviorInterface) {
@@ -1137,6 +1141,7 @@ class JavaScriptBackend extends Backend {
     Registry registry = compiler.globalDependencies;
     enqueue(enqueuer, getNativeInterceptorMethod, registry);
     enqueueClass(enqueuer, jsPlainJavaScriptObjectClass, registry);
+    enqueueClass(enqueuer, jsJavaScriptFunctionClass, registry);
     needToInitializeIsolateAffinityTag = true;
     needToInitializeDispatchProperty = true;
   }
@@ -1272,7 +1277,7 @@ class JavaScriptBackend extends Backend {
     if (!type.treatAsRaw || type.containsTypeVariables) {
       enqueueClass(world, compiler.listClass, registry);
     }
-    if (type.element != null && type.element.isNative) {
+    if (type.element != null && (type.element.isNative || type.element.isJsInterop)) {
       // We will neeed to add the "$is" and "$as" properties on the
       // JavaScript object prototype, so we make sure
       // [:defineProperty:] is compiled.
@@ -1468,7 +1473,7 @@ class JavaScriptBackend extends Backend {
 
   ClassElement defaultSuperclass(ClassElement element) {
     // Native classes inherit from Interceptor.
-    return element.isNative ? jsInterceptorClass : compiler.objectClass;
+    return (element.isNative || element.isJsInterop) ? jsInterceptorClass : compiler.objectClass;
   }
 
   /**
@@ -2099,6 +2104,7 @@ class JavaScriptBackend extends Backend {
         jsExtendableArrayClass = findClass('JSExtendableArray');
         jsUnmodifiableArrayClass = findClass('JSUnmodifiableArray');
         jsPlainJavaScriptObjectClass = findClass('PlainJavaScriptObject');
+        jsJavaScriptFunctionClass = findClass('JavaScriptFunction');
         jsUnknownJavaScriptObjectClass = findClass('UnknownJavaScriptObject');
         jsIndexableClass = findClass('JSIndexable');
         jsMutableIndexableClass = findClass('JSMutableIndexable');
@@ -3002,7 +3008,7 @@ class JavaScriptResolutionCallbacks extends ResolutionCallbacks {
           backend.find(backend.jsHelperLibrary, 'functionTypeTestMetaHelper'),
           registry);
     }
-    if (type.element != null && type.element.isNative) {
+    if (type.element != null && (type.element.isNative || type.element.isJsInterop)) {
       // We will neeed to add the "$is" and "$as" properties on the
       // JavaScript object prototype, so we make sure
       // [:defineProperty:] is compiled.