Change the default for the len argument to writeFrom on OutputStream

runtime/bin/file_impl.dart

Index: runtime/bin/file_impl.dart
diff --git a/runtime/bin/file_impl.dart b/runtime/bin/file_impl.dart
index 6dbd6f921b708394ccb73c919d8c5f35ce8fc6b3..8225de2862dc7018c3bfd38d8e6e9036e4d7eb30 100644
--- a/runtime/bin/file_impl.dart
+++ b/runtime/bin/file_impl.dart
@@ -73,12 +73,13 @@ class _FileOutputStream implements FileOutputStream {
     _file.openSync(true);
   }
 
-  bool write(List<int> buffer) {
+  bool write(List<int> buffer, [bool copyBuffer = false]) {
     return _write(buffer, 0, buffer.length);
   }
 
   bool writeFrom(List<int> buffer, [int offset, int len]) {
-    return _write(buffer, offset, (len == null) ? buffer.length : len);
+    return _write(
+        buffer, offset, (len == null) ? buffer.length - offset : len);
   }
 
   void end() {