Support checking of malbounded types.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 6bf50f821904696df098197feb0f32c52f4a1eb3..24c982d6a618b64b0b511090ae059d24fa9d7ecf 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1077,6 +1077,16 @@ class JavaScriptBackend extends Backend {
     enqueueClass(compiler.enqueuer.resolution, compiler.stringClass, elements);
   }
 
+  void registerTypeVariableBoundsSubtypeCheck(DartType typeArgument,
+                                              DartType bound) {
+    rti.registerTypeVariableBoundsSubtypeCheck(typeArgument, bound);
+  }
+
+  void registerTypeVariableBoundCheck(TreeElements elements) {
+    enqueueInResolution(getThrowTypeError(), elements);
+    enqueueInResolution(getAssertIsSubtype(), elements);
+  }
+
   void registerAbstractClassInstantiation(TreeElements elements) {
     enqueueInResolution(getThrowAbstractClassInstantiationError(), elements);
     // Also register the types of the arguments passed to this method.
@@ -1482,6 +1492,10 @@ class JavaScriptBackend extends Backend {
     return compiler.findHelper('throwRuntimeError');
   }
 
+  Element getThrowTypeError() {
+    return compiler.findHelper('throwTypeError');
+  }
+
   Element getThrowAbstractClassInstantiationError() {
     return compiler.findHelper('throwAbstractClassInstantiationError');
   }
@@ -1534,6 +1548,10 @@ class JavaScriptBackend extends Backend {
     return compiler.findHelper('runtimeTypeToString');
   }
 
+  Element getAssertIsSubtype() {
+    return compiler.findHelper('assertIsSubtype');
+  }
+
   Element getCheckSubtype() {
     return compiler.findHelper('checkSubtype');
   }