Change restrictions on start/end on String.fromCharCodes.

sdk/lib/core/string.dart

Index: sdk/lib/core/string.dart
diff --git a/sdk/lib/core/string.dart b/sdk/lib/core/string.dart
index 9813ad0569c4f41ae957ac23930a9f1370fd5eb5..90e6b508b6b14eacbb5985033be2aa3814879207 100644
--- a/sdk/lib/core/string.dart
+++ b/sdk/lib/core/string.dart
@@ -106,13 +106,10 @@ abstract class String implements Comparable<String>, Pattern {
    *     clef.codeUnitAt(0); // 0xD834
    *     clef.codeUnitAt(1); // 0xDD1E
    *
-   * If [start] is provided, the first `start` elements of `charCodes` are
-   * skipped. If `charCodes` has fewer than `start` elements in all, the
-   * result is an empty string. The `start` value must be non-negative.
-   *
-   * If [end] is provided, any elements of `charCodes` after the `end`'th are
-   * ignored. If `charCodes` has fewer than `end` elements, the `end` parameter
-   * has no effect.
+   * If [start] and [end] is provided, only the values of [charCodes]
+   * at positions from `start` to, but not including, `end`, are used.
+   * The `start` and `end` values must satisfy
+   * `0 <= start <= end <= charCodes.length`.
    */
   external factory String.fromCharCodes(Iterable<int> charCodes,
                                         [int start = 0, int end]);