Optimize List.toList/.sublist and List.from on lists.

runtime/lib/growable_array.dart

Index: runtime/lib/growable_array.dart
diff --git a/runtime/lib/growable_array.dart b/runtime/lib/growable_array.dart
index 1a7b88270d35f3dce5a42bc974fba881ea738423..56e70b260e251b5d0fd063ef5eabbcba35813db2 100644
--- a/runtime/lib/growable_array.dart
+++ b/runtime/lib/growable_array.dart
@@ -103,10 +103,11 @@ class _GrowableList<T> implements List<T> {
     if (end == null) end = this.length;
     int length = end - start;
     if (start == end) return <T>[];
-    List list = new _GrowableList<T>.withCapacity(length);
-    list.length = length;
+    List list = new _List(length);
     Lists.copy(this, start, list, 0, length);
-    return list;
+    var result = new _GrowableList<T>.withData(list);
+    result._setLength(length);
+    return result;
   }
 
   static const int _kDefaultCapacity = 2;
@@ -336,7 +337,10 @@ class _GrowableList<T> implements List<T> {
   }
 
   List<T> toList({ bool growable: true }) {
-    return new List<T>.from(this, growable: growable);
+    var length = this.length;
+    var result = growable ? new _GrowableList<T>(length) : new _List<T>(length);
+    Lists.copy(this, 0, result, 0, length);
+    return result;
   }
 
   Set<T> toSet() {