Fix argument processing for RandomAccessFile.writeFrom

sdk/lib/io/file_impl.dart

Index: sdk/lib/io/file_impl.dart
diff --git a/sdk/lib/io/file_impl.dart b/sdk/lib/io/file_impl.dart
index 2dac1b84d7e65a741a43b8423456b621fc2807ab..72731b2ff3be1cf039c39f31116d3e4b7041a81f 100644
--- a/sdk/lib/io/file_impl.dart
+++ b/sdk/lib/io/file_impl.dart
@@ -772,7 +772,10 @@ class _RandomAccessFile
         (end != null && end is !int)) {
       throw new ArgumentError("Invalid arguments to writeFrom");
     }
-
+    if (start == null) start = 0;

[Lasse Reichstein Nielsen, 2015/05/26 11:20:12]

Why not just make 0 the default value for the `start` parameter directly, as we
do everywhere else?

Then you probably want to just do:
  
  end = RangeError.checkValidRange(start, end, this);
  if (start == end) return;

as the entire prelude of the function.

In other words, drop the _checkReadWriteListArguments function, and don't do the
end = buffer.length manually (it's done in RangeError.checkValidRange too).

[Søren Gjesse, 2015/05/26 14:51:15]

Done. _checkReadWriteListArguments actually just called
RangeError.checkValidRange

Fixed for readInto and readIntoSync as well.

+    if (end == null) end = buffer.length;
+    if (end == start) return;
+    _checkReadWriteListArguments(buffer.length, start, end);
     _BufferAndStart result;
     try {
       result = _ensureFastAndSerializableByteData(buffer, start, end);