Add WhereIterable.map

sdk/lib/internal/iterable.dart

Index: sdk/lib/internal/iterable.dart
diff --git a/sdk/lib/internal/iterable.dart b/sdk/lib/internal/iterable.dart
index 2bedb48e64644e190efdf3dd1a650af2c097a524..0e7b171e26002c4aa73f57516a1b7246196dee82 100644
--- a/sdk/lib/internal/iterable.dart
+++ b/sdk/lib/internal/iterable.dart
@@ -426,6 +426,10 @@ class WhereIterable<E> extends Iterable<E> {
   WhereIterable(this._iterable, bool this._f(E element));
 
   Iterator<E> get iterator => new WhereIterator<E>(_iterable.iterator, _f);
+
+  // Specialization of [Iterable.map] to non-EfficientLength.
+  Iterable/*<T>*/ map/*<T>*/(/*=T*/ f(E element)) =>
+     new MappedIterable<E, dynamic/*=T*/>._(this, f);

[Lasse Reichstein Nielsen, 2016/09/21 07:17:13]

I don't see why this makes any difference - the method is completely identical
to the one inherited from Iterable?
There is nothing about EfficientLength in the Iterable version either.

[sra1, 2016/09/21 16:26:22]

The difference is
new MappedIterable<E, T>(this, f)
new MappedIterable<E, T>._(this, f)

The former has the expensive type test and two classes in the return type, and
cannot be inlined by dart2js (too big)
The latter has no type test and a single class in the return type which enables
further optimizations and/or inlining

[Lasse Reichstein Nielsen, 2016/09/21 19:42:16]

Ah, I completely missed that difference :)

 }
 
 class WhereIterator<E> extends Iterator<E> {