Don't always call _copyFromObjectArray.

runtime/lib/array.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 // TODO(srdjan): Use shared array implementation.
 class _List<E> implements List<E> {
 
   factory _List(length) native "List_allocate";
 
   E operator [](int index) native "List_getIndexed";
 
   void operator []=(int index, E value) native "List_setIndexed";
 
   String toString() {
     return ListBase.listToString(this);
   }
 
   int get length native "List_getLength";
 
   void _copyFromObjectArray(_List src,
                             int srcStart,
                             int dstStart,
-                            int count)
+                            int count) {
+    if (count < 128) {
+      for (int i = 0; i < count; i++) {
+        this[dstStart + i] = src[srcStart + i];
+      }
+    } else {
+      _copyFromObjectArrayInternal(src, srcStart, dstStart, count);
+    }
+  }
+
+  void _copyFromObjectArrayInternal(_List src,
+                                    int srcStart,
+                                    int dstStart,
+                                    int count)
       native "List_copyFromObjectArray";
 
   void insert(int index, E element) {
     throw NonGrowableListError.add();
   }
 
   void insertAll(int index, Iterable<E> iterable) {
     throw NonGrowableListError.add();
   }
 
@@ skipping 24 matching lines @@
   // List interface.
   void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]) {
     if (start < 0 || start > this.length) {
       throw new RangeError.range(start, 0, this.length);
     }
     if (end < start || end > this.length) {
       throw new RangeError.range(end, start, this.length);
     }
     int length = end - start;
     if (length == 0) return;
-
-    if (ClassID.getID(iterable) == ClassID.cidOneByteString) {
+    if (identical(this, iterable)) {
+      Lists.copy(iterable, skipCount, this, start, length);
+    } else if (ClassID.getID(iterable) == ClassID.cidArray) {
       _copyFromObjectArray(iterable, skipCount, start, length);
+    } else if (iterable is List) {
+      Lists.copy(iterable, skipCount, this, start, length);
     } else {
-      if (iterable is List) {
-        Lists.copy(iterable, skipCount, this, start, length);
-      } else {
-        Iterator it = iterable.iterator;
-        while (skipCount > 0) {
-          if (!it.moveNext()) return;
-          skipCount--;
-        }
-        for (int i = start; i < end; i++) {
-          if (!it.moveNext()) return;
-          this[i] = it.current;
-        }
+      Iterator it = iterable.iterator;
+      while (skipCount > 0) {
+        if (!it.moveNext()) return;
+        skipCount--;
+      }
+      for (int i = start; i < end; i++) {
+        if (!it.moveNext()) return;
+        this[i] = it.current;
       }
     }
   }
 
   void removeRange(int start, int end) {
     throw NonGrowableListError.remove();
   }
 
   void replaceRange(int start, int end, Iterable<E> iterable) {
     throw NonGrowableListError.remove();
@@ skipping 463 matching lines @@
   bool moveNext() {
     if (_index >= _length) {
       _current = null;
       return false;
     }
     _current = _array[_index];
     _index++;
     return true;
   }
 }