Implement type argument access and reification of runtime types.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
index fd1f21d09bde30b70c2ea1006da5416c718943dc..1ee1b802bb4d260d0cf6f62d0baa55d7964a6ea1 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
@@ -857,14 +857,15 @@ abstract class IrBuilderVisitor extends ResolvedVisitor<ir.Primitive>
 
     DartType type = elements.getTypeLiteralType(node);
     if (type is TypeVariableType) {
-      ir.Primitive prim = new ir.ReifyTypeVar(type.element);
-      irBuilder.add(new ir.LetPrim(prim));
-      return prim;
+      return buildReifyTypeVariable(irBuilder.buildThis(), type);
     } else {
       return translateConstant(node);
     }
   }
 
+  ir.Primitive buildReifyTypeVariable(ir.Primitive target,
+                                      TypeVariableType variable);
+
   ir.Primitive visitSendSet(ast.SendSet node) {
     assert(irBuilder.isOpen);
     Element element = elements[node];
@@ -1278,6 +1279,15 @@ class DartIrBuilderVisitor extends IrBuilderVisitor {
       List<ir.Primitive> arguments) {
     return arguments;
   }
+
+  @override
+  ir.Primitive buildReifyTypeVariable(ir.Primitive target,
+                                      TypeVariableType variable) {
+    assert(target is ir.This);
+    ir.Primitive prim = new ir.ReifyTypeVar(variable.element);
+    irBuilder.add(new ir.LetPrim(prim));
+    return prim;
+  }
 }
 
 /// IR builder specific to the JavaScript backend, coupled to the [JsIrBuilder].
@@ -1803,6 +1813,16 @@ class JsIrBuilderVisitor extends IrBuilderVisitor {
     }
     return result;
   }
+
+  @override
+  ir.Primitive buildReifyTypeVariable(ir.Primitive target,
+                                      TypeVariableType variable) {
+    ir.Primitive typeArgument = new ir.ReadTypeVariable(variable, target);
+    irBuilder.add(new ir.LetPrim(typeArgument));
+    ir.Primitive type = new ir.ReifyRuntimeType(typeArgument);
+    irBuilder.add(new ir.LetPrim(type));
+    return type;
+  }
 }
 
 /// Interface for generating [SourceInformation] for the CPS.