None of these operating systems are fuchsia

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # =============================================================================
 # PLATFORM SELECTION
 # =============================================================================
 #
 # There are two main things to set: "os" and "cpu". The "toolchain" is the name
 # of the GN thing that encodes combinations of these things.
@@ skipping 250 matching lines @@
 #   generally too different despite being based on the Linux kernel).
 #
 # Do not add more is_* variants here for random lesser-used Unix systems like
 # aix or one of the BSDs. If you need to check these, just check the
 # current_os value directly.
 
 if (current_os == "win" || current_os == "winrt_81" ||
     current_os == "winrt_81_phone" || current_os == "winrt_10") {
   is_android = false
   is_chromeos = false
+  is_fuchsia = false
   is_ios = false
   is_linux = false
   is_mac = false
   is_nacl = false
   is_posix = false
   is_win = true
 } else if (current_os == "mac") {
   is_android = false
+  is_fuchsia = false
   is_chromeos = false
   is_ios = false
   is_linux = false
   is_mac = true
   is_nacl = false
   is_posix = true
   is_win = false
 } else if (current_os == "android") {
   is_android = true
+  is_fuchsia = false
   is_chromeos = false
   is_ios = false
   is_linux = false
   is_mac = false
   is_nacl = false
   is_posix = true
   is_win = false
 } else if (current_os == "chromeos") {
   is_android = false
+  is_fuchsia = false
   is_chromeos = true
   is_ios = false
   is_linux = true
   is_mac = false
   is_nacl = false
   is_posix = true
   is_win = false
 } else if (current_os == "nacl") {
   # current_os == "nacl" will be passed by the nacl toolchain definition.
   # It is not set by default or on the command line. We treat is as a
   # Posix variant.
   is_android = false
   is_chromeos = false
+  is_fuchsia = false
   is_ios = false
   is_linux = false
   is_mac = false
   is_nacl = true
   is_posix = true
   is_win = false
 } else if (current_os == "ios") {
   is_android = false
   is_chromeos = false
+  is_fuchsia = false
   is_ios = true
   is_linux = false
   is_mac = false
   is_nacl = false
   is_posix = true
   is_win = false
 } else if (current_os == "linux") {
   is_android = false
   is_chromeos = false
+  is_fuchsia = false
   is_ios = false
   is_linux = true
   is_mac = false
   is_nacl = false
   is_posix = true
   is_win = false
 }
 
 # =============================================================================
 # SOURCES FILTERS
@@ skipping 292 matching lines @@
 set_defaults("component") {
   if (is_component_build) {
     configs = default_shared_library_configs
     if (is_android) {
       configs -= [ "//build/config/android:hide_native_jni_exports" ]
     }
   } else {
     configs = default_compiler_configs
   }
 }