Introduce (private) ZLibFilter to dart:io.

runtime/third_party/zlib/LICENSE

Index: runtime/third_party/zlib/LICENSE
diff --git a/runtime/third_party/zlib/LICENSE b/runtime/third_party/zlib/LICENSE
new file mode 100644
index 0000000000000000000000000000000000000000..c1fbf214986ebb1cdf78de4ad395fb1ec1a97570
--- /dev/null
+++ b/runtime/third_party/zlib/LICENSE
@@ -0,0 +1,25 @@
+/* zlib.h -- interface of the 'zlib' general purpose compression library

[Søren Gjesse, 2012/10/25 13:54:45]

I think you also need to update the LICENSE file in the repository root
(http://code.google.com/p/dart/source/browse/branches/bleeding_edge/LICENSE).

+  version 1.2.7, May 2nd, 2012
+
+  Copyright (C) 1995-2012 Jean-loup Gailly and Mark Adler
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Jean-loup Gailly        Mark Adler
+  jloup@gzip.org          madler@alumni.caltech.edu
+
+*/