Really remove io support when dart:io is unsupported.

runtime/bin/BUILD.gn

 # Copyright (c) 2014, 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.
 
 
 declare_args() {
   dart_io_support = false
 }
 
 
@@ skipping 173 matching lines @@
   ]
 
   sources = [
     "address_sanitizer.cc",
     "gen_snapshot.cc",
     # Very limited native resolver provided.
     "builtin_common.cc",
     "builtin_gen_snapshot.cc",
     "builtin.cc",
     "builtin.h",
-    "platform_android.cc",
-    "platform_linux.cc",
-    "platform_macos.cc",
-    "platform_win.cc",
-    "platform.h",
     "vmservice_impl.cc",
     "vmservice_impl.h",
     # Include generated source files.
     "$target_gen_dir/builtin_gen.cc",
     "$target_gen_dir/io_gen.cc",
     "$target_gen_dir/io_patch_gen.cc",
     "$target_gen_dir/resources_gen.cc",
   ]
 
   include_dirs = [
@@ skipping 15 matching lines @@
                 [ rebase_path("io_impl_sources.gypi") ],
                 "scope",
                 [ "io_impl_sources.gypi" ])
 
 
 # A source set for the implementation of 'dart:io' library
 # (without secure sockets) suitable for linking with gen_snapshot.
 source_set("gen_snapshot_dart_io") {
   configs += ["..:dart_config",]
 
-  # Set custom sources assignment filter. The custom filters does three things:
-  # 1) Filters out unnecessary files pulled in from the gypi files.
-  # 2) Filters out secure socket support.
-  # 3) Enables dart:io by filtering out _unsupported.cc implementations.
+  deps = [
+    "//third_party/zlib",
+  ]
+
   custom_sources_filter = [
-    "*net/nss_memio.cc",
-    "*net/nss_memio.h",
-    "*root_certificates.cc",
-    "*secure_socket_boringssl.cc",
-    "*secure_socket_boringssl.h",
-    "*secure_socket_macos.cc",
-    "*secure_socket_macos.h",
-    "*secure_socket.h",
-    "filter.cc",
-    "*io_service_unsupported.cc",
-    "platform_*.cc",
-    "*io_service.cc",
-    "*io_service.h",
     "*_test.cc",
     "*_test.h",
-    "*dbg*",
     "builtin.cc",
     "builtin_common.cc",
     "builtin_gen_snapshot.cc",
   ]
   if (!is_mac && !is_ios) {
     # Dart tree uses *_macos.* instead of *_mac.*
     custom_sources_filter += [
       "*_macos.h",
       "*_macos.cc",
     ]
   }
   set_sources_assignment_filter(custom_sources_filter)
 
   defines = [ "DART_IO_SECURE_SOCKET_DISABLED" ]
 
   sources = io_impl_sources_gypi.sources + builtin_impl_sources_gypi.sources
   sources += [
     "io_natives.cc",
     "io_natives.h",
-    "log_android.cc",
-    "log_linux.cc",
-    "log_macos.cc",
-    "log_win.cc",
-    "log.h",
   ]
 
   include_dirs = [
     "..",
     "//third_party"
   ]
 }
 
 # A source set for the implementation of 'dart:io' library
 # (without secure sockets).
 source_set("embedded_dart_io") {
   configs += ["..:dart_config",]
 
-  # Set custom sources assignment filter. The custom filters does three things:
-  # 1) Filters out unnecessary files pulled in from the gypi files.
-  # 2) Filters out secure socket support.
-  # 3) Enables dart:io by filtering out _unsupported.cc implementations.
   custom_sources_filter = [
-    "*net/nss_memio.cc",
-    "*net/nss_memio.h",
-    "*root_certificates.cc",
-    "*secure_socket_boringssl.cc",
-    "*secure_socket_boringssl.h",
-    "*secure_socket_macos.cc",
-    "*secure_socket_macos.h",
-    "*secure_socket.h",
-    "*filter_unsupported.cc",
-    "*io_service_unsupported.cc",
-    "*io_service.cc",
-    "*io_service.h",
     "*_test.cc",
     "*_test.h",
-    "*dbg*",
     "builtin.cc",
     "builtin_gen_snapshot.cc",
   ]
   if (!is_mac && !is_ios) {
     # Dart tree uses *_macos.* instead of *_mac.*
     custom_sources_filter += [
       "*_macos.h",
       "*_macos.cc",
     ]
   }
@@ skipping 14 matching lines @@
     "log_macos.cc",
     "log_win.cc",
     "log.h",
   ]
 
   include_dirs = [
     "..",
     "//third_party"
   ]
 }