Fixes for using _DeferredClassElement and SDK summary.

pkg/analyzer/lib/src/dart/element/element.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 661 matching lines @@
         visitedClasses = <ClassElementImpl>[this];
       } else {
         if (visitedClasses.contains(this)) {
           // Loop in the class hierarchy.  Don't try to forward any
           // constructors.
           return <ConstructorElement>[];
         }
         visitedClasses.add(this);
       }
       try {
-        ClassElement superclass = supertype.element;
-        if (superclass is ClassElementHandle) {
-          superclass = (superclass as ClassElementHandle).actualElement;
-        }
-        constructorsToForward = (superclass as ClassElementImpl)
+        constructorsToForward = getImpl(supertype.element)
             ._computeMixinAppConstructors(visitedClasses);
       } finally {
         visitedClasses.removeLast();
       }
     }
 
     // Figure out the type parameter substitution we need to perform in order
     // to produce constructors for this class.  We want to be robust in the
     // face of errors, so drop any extra type arguments and fill in any missing
     // ones with `dynamic`.
@@ skipping 41 matching lines @@
       return implicitConstructor;
     }).toList();
   }
 
   PropertyAccessorElement _internalLookUpConcreteGetter(
       String getterName, LibraryElement library, bool includeThisClass) {
     PropertyAccessorElement getter =
         _internalLookUpGetter(getterName, library, includeThisClass);
     while (getter != null && getter.isAbstract) {
       Element definingClass = getter.enclosingElement;
-      if (definingClass is! ClassElementImpl) {
+      if (definingClass is! ClassElement) {
         return null;
       }
-      getter = (definingClass as ClassElementImpl)
+      getter = getImpl(definingClass)
           ._internalLookUpGetter(getterName, library, false);
     }
     return getter;
   }
 
   MethodElement _internalLookUpConcreteMethod(
       String methodName, LibraryElement library, bool includeThisClass) {
     MethodElement method =
         _internalLookUpMethod(methodName, library, includeThisClass);
     while (method != null && method.isAbstract) {
@@ skipping 139 matching lines @@
       }
     }
     supertypes = classElt.mixins;
     for (int i = 0; i < supertypes.length; i++) {
       if (_safeIsOrInheritsProxy(supertypes[i].element, visitedClassElts)) {
         return true;
       }
     }
     return false;
   }
+
+  /**
+   * Return the [ClassElementImpl] of the given [classElement].  May throw an
+   * exception if the [ClassElementImpl] cannot be provided (should not happen
+   * though).
+   */
+  static ClassElementImpl getImpl(ClassElement classElement) {
+    if (classElement is ClassElementHandle) {
+      return getImpl(classElement.actualElement);
+    }
+    return classElement as ClassElementImpl;
+  }
 }
 
 /**
  * A concrete implementation of a [CompilationUnitElement].
  */
 class CompilationUnitElementImpl extends UriReferencedElementImpl
     implements CompilationUnitElement {
   /**
    * The source that corresponds to this compilation unit.
    */
@@ skipping 4029 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }