Support transforming the exception in Future.transform().

lib/core/future.dart

Index: lib/core/future.dart
diff --git a/lib/core/future.dart b/lib/core/future.dart
index 6b2fa19e3e82b3c5abb094af4f21570117fab0a5..db238ec4057dcded2d97b9be96ee50220c7586e3 100644
--- a/lib/core/future.dart
+++ b/lib/core/future.dart
@@ -104,8 +104,16 @@ interface Future<T> default FutureImpl<T> {
    *
    * You must not add exception handlers to [this] future prior to calling
    * transform, and any you add afterwards will not be invoked.
+   *
+   * The [onException] parameter can be provided to control how exceptions
+   * received by this future or the transformation are handled. If an exception
+   * occures, [onException] will be called. If that throws an exception, the
+   * returned future will complete with that exception. If it returns `true`,
+   * then the exception is considered handled and is not propogated to the
+   * returned future. If it returns anything else, the original exception will
+   * be propogated.
    */
-  Future transform(transformation(T value));
+  Future transform(transformation(T value), [onException(Object exception)]);

[Siggi Cherem (dart-lang), 2012/09/04 16:56:33]

maybe use [bool onException(Object exception)]?
(add bool type?)

 
    /**
     * A future representing an asynchronous transformation applied to this