Fix a couple of doc comment references - and many spelling mistakes

sdk/lib/convert/base64.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.convert;
 
 /**
  * A [base64](https://tools.ietf.org/html/rfc4648) encoder and decoder.
  *
  * It encodes using the default base64 alphabet,
@@ skipping 378 matching lines @@
    * value (a string), the buffer can be reused between chunks.
    */
   Uint8List bufferCache;
 
   _BufferCachingBase64Encoder(bool urlSafe) : super(urlSafe);
 
   Uint8List createBuffer(int bufferLength) {
     if (bufferCache == null || bufferCache.length < bufferLength) {
       bufferCache = new Uint8List(bufferLength);
     }
-    // Return a view of the buffer, so it has the reuested length.
+    // Return a view of the buffer, so it has the requested length.
     return new Uint8List.view(bufferCache.buffer, 0, bufferLength);
   }
 }
 
 abstract class _Base64EncoderSink extends ByteConversionSinkBase {
   void add(List<int> source) {
     _add(source, 0, source.length, false);
   }
 
   void close() {
@@ skipping 125 matching lines @@
    * contain a full block, the decoded bits (six per character) of the
    * available characters are stored in [_state] until the next call to
    * [_decode] or [_close].
    *
    * If no padding has been seen, the value is
    *   `numberOfCharactersSeen | (decodedBits << 2)`
    * where `numberOfCharactersSeen` is between 0 and 3 and decoded bits
    * contains six bits per seen character.
    *
    * If padding has been seen the value is negative. It's the bitwise negation
-   * of the number of remanining allowed padding characters (always ~0 or ~1).
+   * of the number of remaining allowed padding characters (always ~0 or ~1).
    *
    * A state of `0` or `~0` are valid places to end decoding, all other values
    * mean that a four-character block has not been completed.
    */
   int _state = 0;
 
   /**
    * Encodes [count] and [bits] as a value to be stored in [_state].
    */
   static int _encodeCharacterState(int count, int bits) {
@@ skipping 306 matching lines @@
     end = RangeError.checkValidRange(start, end, string.length);
     if (start == end) return;
     Uint8List buffer = _decoder.decode(string, start, end);
     if (buffer != null) _sink.add(buffer);
     if (isLast) {
       _decoder.close(string, end);
       _sink.close();
     }
   }
 }