Add KernelWorldBuilder and KElement model.

pkg/compiler/lib/src/kernel/element_adapter.dart

Index: pkg/compiler/lib/src/kernel/element_adapter.dart
diff --git a/pkg/compiler/lib/src/kernel/element_adapter.dart b/pkg/compiler/lib/src/kernel/element_adapter.dart
index 15d7e0e96e4d8de0194e17b23f5bc7550190bd2d..43aae2db3e69fbc44cdd6e26a4badd6a94a45c87 100644
--- a/pkg/compiler/lib/src/kernel/element_adapter.dart
+++ b/pkg/compiler/lib/src/kernel/element_adapter.dart
@@ -140,7 +140,8 @@ abstract class KernelElementAdapterMixin implements KernelElementAdapter {
     if (node is ir.PropertySet) return getSetterSelector(node);
     if (node is ir.InvocationExpression) return getInvocationSelector(node);
     throw new SpannableAssertionFailure(CURRENT_ELEMENT_SPANNABLE,
-        "Can only get the selector for a property get or an invocation: ${node}");
+        "Can only get the selector for a property get or an invocation: "
+        "${node}");
   }
 
   Selector getInvocationSelector(ir.InvocationExpression invocation) {