Add some ArgumentError and RangeError constructors that capture more information.

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 8c8f8f042578db44fd548a8d6d220cb892d97209..b95c6e146a6ed9fe0d44573804ec7d3b384facaa 100644
--- a/sdk/lib/core/string.dart
+++ b/sdk/lib/core/string.dart
@@ -678,7 +678,7 @@ class RuneIterator implements BidirectionalIterator<int> {
    */
   void set rawIndex(int rawIndex) {
     if (rawIndex >= string.length) {
-      throw new RangeError.range(rawIndex, 0, string.length - 1);
+      throw new RangeError.index(rawIndex, string);
     }
     reset(rawIndex);
     moveNext();