Introduce (private) ZLibFilter to dart:io.

runtime/third_party/zlib/INDEX

Index: runtime/third_party/zlib/INDEX
diff --git a/runtime/third_party/zlib/INDEX b/runtime/third_party/zlib/INDEX
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+CMakeLists.txt  cmake build file
+ChangeLog       history of changes
+FAQ             Frequently Asked Questions about zlib
+INDEX           this file
+Makefile        dummy Makefile that tells you to ./configure
+Makefile.in     template for Unix Makefile
+README          guess what
+configure       configure script for Unix
+make_vms.com    makefile for VMS
+test/example.c  zlib usages examples for build testing
+test/minigzip.c minimal gzip-like functionality for build testing
+test/infcover.c inf*.c code coverage for build coverage testing
+treebuild.xml   XML description of source file dependencies
+zconf.h.cmakein zconf.h template for cmake
+zconf.h.in      zconf.h template for configure
+zlib.3          Man page for zlib
+zlib.3.pdf      Man page in PDF format
+zlib.map        Linux symbol information
+zlib.pc.in      Template for pkg-config descriptor
+zlib.pc.cmakein zlib.pc template for cmake
+zlib2ansi       perl script to convert source files for C++ compilation
+
+amiga/          makefiles for Amiga SAS C
+as400/          makefiles for AS/400
+doc/            documentation for formats and algorithms
+msdos/          makefiles for MSDOS
+nintendods/     makefile for Nintendo DS
+old/            makefiles for various architectures and zlib documentation
+                files that have not yet been updated for zlib 1.2.x
+qnx/            makefiles for QNX
+watcom/         makefiles for OpenWatcom
+win32/          makefiles for Windows
+
+                zlib public header files (required for library use):
+zconf.h
+zlib.h
+
+                private source files used to build the zlib library:
+adler32.c
+compress.c
+crc32.c
+crc32.h
+deflate.c
+deflate.h
+gzclose.c
+gzguts.h
+gzlib.c
+gzread.c
+gzwrite.c
+infback.c
+inffast.c
+inffast.h
+inffixed.h
+inflate.c
+inflate.h
+inftrees.c
+inftrees.h
+trees.c
+trees.h
+uncompr.c
+zutil.c
+zutil.h
+
+                source files for sample programs
+See examples/README.examples
+
+                unsupported contributions by third parties
+See contrib/README.contrib