Insert checks before deferred calls and accesses.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

Index: sdk/lib/_internal/compiler/implementation/elements/elements.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/elements.dart b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
index d3dd0309130229ec5021a63f112533f6c26c2fc6..282c7c5ec84262ce9845643204e8e3b942f128a0 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/elements.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/elements.dart
@@ -831,6 +831,10 @@ abstract class FunctionElement extends Element
 
   bool get isRedirectingFactory;
 
+  /// Used to retrieve a link to the abstract field element representing this
+  /// element.
+  AbstractFieldElement get abstractField;
+
   /**
    * Compute the type of the target of a constructor for an instantiation site
    * with type [:newType:].
@@ -1053,6 +1057,7 @@ abstract class MetadataAnnotation implements Spannable {
   MetadataAnnotation ensureResolved(Compiler compiler);
 }
 
+// TODO(johnniwinther): Remove this element.
 abstract class VoidElement extends Element {}
 
 /// An [Element] that has a type.