Add KernelWorldBuilder and KElement model.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 405724fa6f91c1d1344a347e353a72861bee3771..ccc2071305295908e9b9f3a874ad536f20773654 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -1559,6 +1559,8 @@ class CompilerDiagnosticReporter extends DiagnosticReporter {
     } else if (node is Local) {
       Local local = node;
       return spanFromElement(local.executableContext);
+    } else if (node is Entity) {
+      return spanFromElement(currentElement);
     } else {
       throw 'No error location.';
     }