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

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index 78d30f784c4881a72821297bc853313251507d91..5ad34037a7cbb8a5e3c2357f8ff7c7b570069f86 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -102,11 +102,12 @@ class _List<E> implements List<E> {
     Lists.indicesCheck(this, start, end);
     if (end == null) end = this.length;
     int length = end - start;
-    if (start == end) return [];
-    List list = new _GrowableList<E>.withCapacity(length);
-    list.length = length;
-    Lists.copy(this, start, list, 0, length);
-    return list;
+    if (start == end) return <E>[];
+    List list = new _List(length);
+    list._copyFromObjectArray(this, start, 0, length);
+    var result = new _GrowableList<E>.withData(list);
+    result._setLength(length);
+    return result;
   }
 
   // Iterable interface.
@@ -249,8 +250,15 @@ class _List<E> implements List<E> {
     throw IterableElementError.tooMany();
   }
 
-  List<E> toList({ bool growable: true}) {
-    return new List<E>.from(this, growable: growable);
+  List<E> toList({ bool growable: true }) {
+    var length = this.length;
+    var result = growable ? new _List(length) : new _List<E>(length);
+    result._copyFromObjectArray(this, 0, 0, length);
+    if (growable) {
+      result = new _GrowableList<E>.withData(result);
+      result._setLength(length);
+    }
+    return result;
   }
 
   Set<E> toSet() {
@@ -340,11 +348,12 @@ class _ImmutableList<E> implements List<E> {
     Lists.indicesCheck(this, start, end);
     if (end == null) end = this.length;
     int length = end - start;
-    if (start == end) return [];
-    List list = new List<E>();
-    list.length = length;
+    if (start == end) return <E>[];
+    List list = new _List(length);
     Lists.copy(this, start, list, 0, length);
-    return list;
+    var result = new _GrowableList<E>.withData(list);
+    result._setLength(length);
+    return result;
   }
 
   Iterable<E> getRange(int start, int end) {
@@ -496,7 +505,10 @@ class _ImmutableList<E> implements List<E> {
   }
 
   List<E> toList({ bool growable: true }) {
-    return new List<E>.from(this, growable: growable);
+    int length = this.length;
+    List list = growable ? new _GrowableList<E>(length) : new _List<E>(length);
+    Lists.copy(this, 0, list, 0, length);
+    return list;
   }
 
   Set<E> toSet() {