Update range errors to agree on the numbers.

sdk/lib/core/errors.dart

Index: sdk/lib/core/errors.dart
diff --git a/sdk/lib/core/errors.dart b/sdk/lib/core/errors.dart
index 0e99b0b271ce48375f613c2fc9522aad6d0e5019..30538071ec3fbde3792917087fe1a2b63df48e3b 100644
--- a/sdk/lib/core/errors.dart
+++ b/sdk/lib/core/errors.dart
@@ -392,12 +392,13 @@ class IndexError extends ArgumentError implements RangeError {
   String get _errorName => "RangeError";

[sra1, 2015/09/09 17:16:05]

Was this supposed to be "IndexError"?

[Lasse Reichstein Nielsen, 2015/09/10 10:08:54]

No, this was introduced as a helper class for a special group of range errors.
It's not important that it's a separate class unless you actually care about it.

   String get _errorExplanation {
     assert(_hasValue);
-    String target = Error.safeToString(indexable);
-    var explanation = ": index should be less than $length";
     if (invalidValue < 0) {
-      explanation = ": index must not be negative";
+      return ": index must not be negative";
     }
-    return explanation;
+    if (length == 0) {
+      return ": no indices are valid";

[sra1, 2015/09/09 17:16:05]

I find this a tiny bit confusing.
It would be nice if the error said the list was empty, but that assumes the
indexable is a List.

[Lasse Reichstein Nielsen, 2015/09/10 10:08:54]

Exactly my problem (and what I started out saying). It does read rather
awkwardly.

Suggestions would be appreciated!

+    }
+    return ": index should be less than $length";
   }
 }