Insert checks before deferred calls and accesses.

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

Index: sdk/lib/_internal/compiler/implementation/elements/modelx.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index 87828ea0989020930d9fa18c86a63e945ffb918d..8b076166c827fc1137cd87de131d925cab9a5052 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -331,6 +331,8 @@ class ErroneousElementX extends ElementX implements ErroneousElement {
 
   isErroneous() => true;
 
+  AbstractFieldElement abstractField;
+
   unsupported() {
     throw 'unsupported operation on erroneous element';
   }
@@ -540,7 +542,7 @@ class ScopeX {
    * element, they are enclosed by the class or compilation unit, as is the
    * abstract field.
    */
-  void addAccessor(Element accessor,
+  void addAccessor(FunctionElementX accessor,
                    Element existing,
                    DiagnosticListener listener) {
     void reportError(Element other) {
@@ -558,6 +560,7 @@ class ScopeX {
         reportError(existing);
       } else {
         AbstractFieldElementX field = existing;
+        accessor.abstractField = field;
         if (accessor.isGetter()) {
           if (field.getter != null && field.getter != accessor) {
             reportError(field.getter);
@@ -575,6 +578,7 @@ class ScopeX {
       Element container = accessor.getEnclosingClassOrCompilationUnit();
       AbstractFieldElementX field =
           new AbstractFieldElementX(accessor.name, container);
+      accessor.abstractField = field;
       if (accessor.isGetter()) {
         field.getter = accessor;
       } else {
@@ -1499,6 +1503,8 @@ class FunctionElementX extends ElementX with AnalyzableElement
 
   final bool _hasNoBody;
 
+  AbstractFieldElement abstractField;
+
   /**
    * If this is a redirecting factory, [defaultImplementation] will be
    * changed by the resolver to point to the redirection target.