Introduce (private) ZLibFilter to dart:io.

runtime/third_party/zlib/zlib.gypi

Index: runtime/third_party/zlib/zlib.gypi
diff --git a/runtime/third_party/zlib/zlib.gypi b/runtime/third_party/zlib/zlib.gypi
new file mode 100644
index 0000000000000000000000000000000000000000..0d553a3d31866b6c5c66e52562e0d3140953ea49
--- /dev/null
+++ b/runtime/third_party/zlib/zlib.gypi
@@ -0,0 +1,50 @@
+# Copyright 2010 Google Inc. All Rights Reserved.
+
+{
+  'targets': [
+    {
+      'target_name': 'libzlib',
+      'type': 'static_library',
+      'dependencies': [
+      ],
+      'include_dirs': [
+        '.',
+      ],
+      'defines': [
+      ],
+      'sources': [
+        'adler32.c',
+        'compress.c',
+        'crc32.c',
+        'crc32.h',
+        'deflate.c',
+        'deflate.h',
+        'infback.c',
+        'inffast.c',
+        'inffast.h',
+        'inffixed.h',
+        'inflate.c',
+        'inflate.h',
+        'inftrees.c',
+        'inftrees.h',
+        'trees.c',
+        'trees.h',
+        'uncompr.c',
+        'zconf.h',
+        'zlib.h',
+        'zutil.c',
+        'zutil.h',
+      ],
+      'cflags': [
+      ],
+      'cflags!': [
+        # Remove C++ only flags.
+        '-Wnon-virtual-dtor',
+        '-Wno-conversion-null',
+        '-fno-rtti',
+        '-fvisibility-inlines-hidden',
+      ],
+    },
+  ],
+}
+