Implement type argument access and reification of runtime types.

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
index 24255022ee55661d1ccd5e8f767b72ff6fa704fd..2e8ace867f7ec4f812dbee52c451901a559df761 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
@@ -125,6 +125,8 @@ class Builder implements cps_ir.Visitor<Node> {
   VariableUse getVariableUse(cps_ir.Reference<cps_ir.Primitive> reference) {
     Variable variable = getVariable(reference.definition);
     if (variable == null) {
+      // Note: this may fail because you forgot to implement a visit-function
+      // in the RegisterAllocator.
       internalError(
           CURRENT_ELEMENT_SPANNABLE,
           "Reference to ${reference.definition} has no register");
@@ -634,5 +636,12 @@ class Builder implements cps_ir.Visitor<Node> {
   Expression visitIsTrue(cps_ir.IsTrue node) {
     return getVariableUse(node.value);
   }
-}
 
+  Expression visitReifyRuntimeType(cps_ir.ReifyRuntimeType node) {
+    return new ReifyRuntimeType(getVariableUse(node.value));
+  }
+
+  Expression visitReadTypeVariable(cps_ir.ReadTypeVariable node) {
+    return new ReadTypeVariable(node.variable, getVariableUse(node.target));
+  }
+}