Add TypeVariable object on runtime to support reflection on type variables.

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 bd8027a881ccaca01be7bb5c90f18ece60e5bda2..5843aeeb305f7f2c84c244bac0ac3a38074a4e24 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -200,6 +200,7 @@ class JavaScriptBackend extends Backend {
   ClassElement typeLiteralClass;
   ClassElement mapLiteralClass;
   ClassElement constMapLiteralClass;
+  ClassElement typeVariableClass;
 
   Element getInterceptorMethod;
   Element interceptedNames;
@@ -406,6 +407,8 @@ class JavaScriptBackend extends Backend {
           checkedModeHelpers,
           key: (helper) => helper.name.slowToString());
 
+  TypeVariableHandler typeVariableHandler;
+
   /// Number of methods compiled before considering reflection.
   int preMirrorsMethodCount = 0;
 
@@ -420,6 +423,7 @@ class JavaScriptBackend extends Backend {
     builder = new SsaBuilderTask(this);
     optimizer = new SsaOptimizerTask(this);
     generator = new SsaCodeGeneratorTask(this);
+    typeVariableHandler = new TypeVariableHandler(this);
   }
 
   static Namer determineNamer(Compiler compiler) {
@@ -665,6 +669,9 @@ class JavaScriptBackend extends Backend {
         new TypeMask.nonNullExact(jsFixedArrayClass));
     extendableArrayType = new HBoundedType(
         new TypeMask.nonNullExact(jsExtendableArrayClass));
+
+    typeVariableClass =
+        compiler.findHelper(const SourceString('TypeVariable'));
   }
 
   void validateInterceptorImplementsAllObjectMethods(
@@ -792,6 +799,10 @@ class JavaScriptBackend extends Backend {
   void registerInstantiatedClass(ClassElement cls,
                                  Enqueuer enqueuer,
                                  TreeElements elements) {
+    if (!cls.typeVariables.isEmpty) {
+      typeVariableHandler.registerClassWithTypeVariables(cls);
+    }
+
     if (!seenAnyClass) {
       seenAnyClass = true;
       if (enqueuer.isResolutionQueue) {
@@ -1854,6 +1865,14 @@ class JavaScriptBackend extends Backend {
       }
       metadataConstants.clear();
     }
+
+    if (isTreeShakingDisabled) {
+      if (enqueuer.isResolutionQueue) {
+        typeVariableHandler.onResolutionQueueEmpty(enqueuer);
+      } else {
+        typeVariableHandler.onCodegenQueueEmpty();
+      }
+    }
   }
 }