Move zlib to //flutter/third_party

Fixes flutter/flutter#146598

Author: jason-simmons

DEPS

@@ -664,7 +664,7 @@ deps = {
   'src/flutter/third_party/wuffs':
    Var('skia_git') + '/external/github.com/google/wuffs-mirror-release-c.git' + '@' + '600cd96cf47788ee3a74b40a6028b035c9fd6a61',
 
-  'src/third_party/zlib':
+  'src/flutter/third_party/zlib':
    Var('chromium_git') + '/chromium/src/third_party/zlib.git' + '@' + '7d77fb7fd66d8a5640618ad32c71fdeb7d3e02df',
 
   'src/flutter/third_party/cpu_features/src':

build/secondary/third_party/zlib/BUILD.gn

@@ -0,0 +1,19 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+group("zlib") {
+  public_deps = [ "//flutter/third_party/zlib" ]
+
+  # Add the third_party root directory to the include path to support Dart
+  # sources that include zlib headers using "zlib/zlib.h"
+  public_configs = [ ":include_third_party" ]
+}
+
+config("zlib_config") {
+  configs = [ "//flutter/third_party/zlib:zlib_config" ]
+}
+
+config("include_third_party") {
+  include_dirs = [ "//flutter/third_party" ]
+}

build/secondary/third_party/zlib/google/BUILD.gn

@@ -0,0 +1,12 @@
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+config("compression_utils_config") {
+  include_dirs = [ "//flutter/third_party/zlib/google" ]
+}
+
+group("compression_utils_portable") {
+  public_deps = [ "//flutter/third_party/zlib/google:compression_utils_portable" ]
+  public_configs = [ ":compression_utils_config" ]
+}