Make String.fromCharCodes take start/end.

sdk/lib/_internal/lib/core_patch.dart

Index: sdk/lib/_internal/lib/core_patch.dart
diff --git a/sdk/lib/_internal/lib/core_patch.dart b/sdk/lib/_internal/lib/core_patch.dart
index 85ab0b9246ffed5c5d9d55d3223eaf31032a5be7..1deb59f6eec490419bd8da1edab486aa4362ca7b 100644
--- a/sdk/lib/_internal/lib/core_patch.dart
+++ b/sdk/lib/_internal/lib/core_patch.dart
@@ -270,11 +270,32 @@ class List<E> {
 @patch
 class String {
   @patch
-  factory String.fromCharCodes(Iterable<int> charCodes) {
-    if (charCodes is! JSArray) {
-      charCodes = new List.from(charCodes);
+  factory String.fromCharCodes(Iterable<int> charCodes,
+                               [int start = 0, int end]) {
+    if (start < 0) start = 0;

[Søren Gjesse, 2014/08/29 11:16:03]

ArgumentError?

[Lasse Reichstein Nielsen, 2014/09/02 07:57:05]

Done.

+    List list;
+    if (charCodes is JSArray) {

[floitsch, 2014/08/29 11:13:20]

does it need to be a JSArray?
Or can we use isJsIndexable? Would that cover the comment in line 279?

[Lasse Reichstein Nielsen, 2014/09/02 07:57:04]

No idea - I was going by the existing code only.

It's worth a try, but I'd keep it in a separate CL.

+      list = charCodes;
+      // If possible, recognize typed lists too.
+      int len = list.length;
+      if (end == null || end > len) end = len;
+      if (start > 0 || end < len) {
+        if (start >= end) return "";
+        charCodes = list.sublist(start, end);

[Lasse Reichstein Nielsen, 2014/09/02 07:57:04]

should be "list = ...".

+      }
+    } else {
+      if (end != null) {
+        if (start >= end) return "";
+        charCodes = charCodes.take(end);
+      }
+      if (start > 0) charCodes = charCodes.skip(start);
+      list = charCodes.toList();  // Try the iterable's own toList first.
+      if (list is! JSArray) {
+        // If that fails, force a JSArray.
+        list = new List.from(charCodes);

[Lasse Reichstein Nielsen, 2014/09/02 07:57:05]

should be .from(list);

+      }
     }
-    return Primitives.stringFromCharCodes(charCodes);
+    return Primitives.stringFromCharCodes(list);
   }
 
   @patch