Optimize int.parse with a radix.

sdk/lib/_internal/compiler/js_lib/core_patch.dart

Index: sdk/lib/_internal/compiler/js_lib/core_patch.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/core_patch.dart b/sdk/lib/_internal/compiler/js_lib/core_patch.dart
index 2de51286d987aea96f8bb9831c395d429cad1ebc..a26ee926e08377f9b1f570e7ca9b910bf7293e9c 100644
--- a/sdk/lib/_internal/compiler/js_lib/core_patch.dart
+++ b/sdk/lib/_internal/compiler/js_lib/core_patch.dart
@@ -272,33 +272,28 @@ class String {
   @patch
   factory String.fromCharCodes(Iterable<int> charCodes,
                                [int start = 0, int end]) {
+    if (start < 0) throw new RangeError.value(start);
     List list;
-    // If possible, recognize typed lists too.
-    if (charCodes is! JSArray) {
-      if (start > 0 || end != null) {
-        if (start < 0) throw new RangeError.value(start);
-        if (end < start) throw new RangeError.value(end);
-        int len = end - start;
-        list = new List.from(charCodes.take(end).skip(start));
-        if (list.length != len) {
-          throw new RangeError.range(end, 0, len);
-        }
-        return Primitives.stringFromCharCodes(list);
+    if (charCodes is JSArray) {
+      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 "";
+        list = list.sublist(start, end);
+      }
+    } 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(list);
       }
-      list = new List.from(charCodes);
-    }
-    int len = list.length;
-    if (start < 0 || start > len) {
-      throw new RangeError.range(start, 0, len);
-    }
-    if (end == null) {
-      end = len;
-    } else if (end < start || end > len) {
-      throw new RangeError.range(end, start, len);
-    }
-
-    if (start > 0 || end < len) {
-      list = list.sublist(start, end);
     }
     return Primitives.stringFromCharCodes(list);
   }