gl: Build drm dependent test only when target_os == "chromeos".

ui/gl/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 use_egl = is_win || is_android || is_linux
 use_glx = use_x11
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
 
-if (is_chromeos) {
+if (target_os == "chromeos") {
   pkg_config("libdrm") {
     packages = [ "libdrm" ]
   }
 }
 
 config("gl_config") {
   defines = []
   if (use_glx) {
     defines += [
       "GL_GLEXT_PROTOTYPES",
@@ skipping 324 matching lines @@
       "test/egl_initialization_displays_unittest.cc",
     ]
   }
 
   if (use_glx) {
     sources += [ "glx_api_unittest.cc" ]
   }
 
   if (use_ozone) {
     sources += [ "gl_image_ozone_native_pixmap_unittest.cc" ]
-    if (is_chromeos && target_cpu != "arm") {
+    if (target_os == "chromeos" && target_cpu != "arm") {
       sources += [ "gl_image_ozone_native_pixmap_drm_unittest.cc" ]
     }
   }
 
   if (is_mac) {
     sources += [ "gl_image_io_surface_unittest.cc" ]
     libs = [ "IOSurface.framework" ]
   }
 
   if (is_win) {
     sources += [ "wgl_api_unittest.cc" ]
   }
 
   include_dirs = [ "//third_party/khronos" ]
 
   deps = [
     ":gl",
     ":gl_unittest_utils",
     ":test_support",
     "//base",
     "//base/test:test_support",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/gl/init",
   ]
 
-  if (is_chromeos) {
+  if (target_os == "chromeos") {
     configs += [ ":libdrm" ]
   }
 
   data_deps = [
     "//third_party/mesa:osmesa",
   ]
 
   if (use_ozone) {
     deps += [ "//ui/ozone" ]
   }
 }
 
 if (is_android) {
   generate_jar_jni("surface_jni_headers") {
     jni_package = "ui/gl"
     classes = [ "android/view/Surface.class" ]
   }
 
   generate_jni("gl_jni_headers") {
     sources = [
       "../android/java/src/org/chromium/ui/gl/SurfaceTextureListener.java",
       "../android/java/src/org/chromium/ui/gl/SurfaceTexturePlatformWrapper.java",
     ]
     public_deps = [
       ":surface_jni_headers",
     ]
     jni_package = "ui/gl"
   }
 }