Add some ArgumentError and RangeError constructors that capture more information.

sdk/lib/convert/ascii.dart

Index: sdk/lib/convert/ascii.dart
diff --git a/sdk/lib/convert/ascii.dart b/sdk/lib/convert/ascii.dart
index 281233a57155200ffa1ed854f323772d63ac6190..40ff5a8fdc14f87afd028987d67d6cfa5fc4c816 100644
--- a/sdk/lib/convert/ascii.dart
+++ b/sdk/lib/convert/ascii.dart
@@ -292,10 +292,10 @@ class _SimpleAsciiDecoderSink extends ByteConversionSinkBase {
   void addSlice(List<int> source, int start, int end, bool isLast) {
     final int length = source.length;
     if (start < 0 || start > length) {
-      throw new RangeError.range(start, 0, length - 1);
+      throw new RangeError.range(start, 0, length);
     }
     if (end < start || end > length) {
-      throw new RangeError.range(end, start, length - 1);
+      throw new RangeError.range(end, start, length);
     }
     if (start < end) {
       if (start != 0 || end != length) {