Revert changes to Future.chain() and Future.transform() from http://codereview.chromium.org/10517006

corelib/src/implementation/future_implementation.dart

 // Copyright 2012 Google Inc. All Rights Reserved.
 // Dart core library.
 
 class FutureImpl<T> implements Future<T> {
 
   bool _isComplete = false;
 
   /**
    * Value that was provided to this Future by the Completer
    */
@@ skipping 140 matching lines @@
     }
     if (_isComplete) {
       throw new FutureAlreadyCompleteException();
     }
     _exception = exception;
     _complete();
   }
 
   Future transform(Function transformation) {
     final completer = new Completer();
-    onComplete((f) {
-      if (!f.hasValue) {
-        completer.completeException(f.exception);
-        return;
-      }
+    handleException((e) {
+      completer.completeException(e);
+      return true;
+    });
+    then((v) {
       var transformed = null;
       try {
-        transformed = transformation(f.value);
+        transformed = transformation(v);
       } catch (final e) {
         completer.completeException(e);
         return;
       }
       completer.complete(transformed);
     });
     return completer.future;
   }
 
   Future chain(Function transformation) {
     final completer = new Completer();
-    onComplete((f) {
-      if (!f.hasValue) {
-        completer.completeException(f.exception);
-        return;
-      }
+    handleException((e) {
+      completer.completeException(e);
+      return true;
+    });
+    then((v) {
       var future = null;
       try {
-        future = transformation(f.value);
+        future = transformation(v);
       } catch (final e) {
         completer.completeException(e);
         return;
       }
-      future.onComplete((g) => g.hasValue
-        ? completer.complete(g.value)
-        : completer.completeException(g.exception));
+      future.handleException((e) {
+        completer.completeException(e);
+        return true;
+      });
+      future.then((b) => completer.complete(b));
     });
     return completer.future;
   }
 }
 
 class CompleterImpl<T> implements Completer<T> {
 
   final FutureImpl<T> _futureImpl;
 
   CompleterImpl() : _futureImpl = new FutureImpl() {}
 
   Future<T> get future() {
     return _futureImpl;
   }
 
   void complete(T value) {
     _futureImpl._setValue(value);
   }
 
   void completeException(var exception) {
     _futureImpl._setException(exception);
   }
 }