Expand is_linux to is_linux || is_chromeos.

Currently is_linux is set to true on Chrome OS build,
but it is planned to be set false. This CL is the preparation
to keep the compatibility.

Bug: chromium:1110266
Test: Build locally.
Change-Id: Ic79a202b0b3baeff157955cd03a07556bfb958a8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/183860
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#32073}

modules/audio_device/BUILD.gn

@@ -263,7 +263,7 @@ rtc_library("audio_device_impl") {
     if (rtc_use_dummy_audio_file_devices) {
       defines += [ "WEBRTC_DUMMY_FILE_DEVICES" ]
     } else {
-      if (is_linux) {
+      if (is_linux || is_chromeos) {
         sources += [
           "linux/alsasymboltable_linux.cc",
           "linux/alsasymboltable_linux.h",
@@ -393,7 +393,7 @@ if (rtc_include_tests) {
       "../utility",
     ]
     absl_deps = [ "//third_party/abseil-cpp/absl/types:optional" ]
-    if (is_linux || is_mac || is_win) {
+    if (is_linux || is_chromeos || is_mac || is_win) {
       sources += [ "audio_device_unittest.cc" ]
     }
     if (is_win) {