fix spelling in core libraries

sdk/lib/convert/html_escape.dart

 // Copyright (c) 2013, 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 `String` converter that converts characters to HTML entities.
  *
- * This is intended to sanitice text before inserting the text into an HTML
+ * This is intended to sanitize text before inserting the text into an HTML
  * document. Characters that are meaningful in HTML are converted to
  * HTML entities (like `&` for `&`).
  *
  * The general converter escapes all characters that are meaningful in HTML
  * attributes or normal element context. Elements with special content types
  * (like CSS or JavaScript) may need a more specialized escaping that
  * understands that content type.
  *
  * If the context where the text will be inserted is known in more detail,
  * it's possible to omit escaping some characters (like quotes when not
@@ skipping 106 matching lines @@
                         this.escapeQuot: false,
                         this.escapeApos: false,
                         this.escapeSlash: false}) : _name = name;
 
   String toString() => _name;
 }
 
 /**
  * Converter which escapes characters with special meaning in HTML.
  *
- * The converter finds characters that are siginificant in HTML source and
+ * The converter finds characters that are significant in HTML source and
  * replaces them with corresponding HTML entities.
  *
  * The characters that need escaping in HTML are:
  *
  * * `&` (ampersand) always need to be escaped.
  * * `<` (less than) and '>' (greater than) when inside an element.
  * * `"` (quote) when inside a double-quoted attribute value.
  * * `'` (apostrophe) when inside a single-quoted attribute value.
  *       Apostrophe is escaped as `&#39;` instead of `&apos;` since
  *       not all browsers understand `&apos;`.
@@ skipping 75 matching lines @@
     if(val == null) {
       _sink.addSlice(chunk, start, end, isLast);
     } else {
       _sink.add(val);
       if (isLast) _sink.close();
     }
   }
 
   void close() { _sink.close(); }
 }