Lacros: Preparation for lacros target_os switch.

This is a mechanical change replacing defined(OS_CHROMEOS) with
BUILDFLAG(IS_CHROMEOS_ASH) to ensure switching lacros' target_os
from linux to chromeos does not affect the lacros binary.

More detail on http://go/lacros-macros.

Bug: 1052397
Change-Id: I2018adb0173f1c0ec56e1f0228bb73fa343da83c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627199Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Yuta Hijikata <ythjkt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843872}

net/cert/nss_cert_database.cc

@@ -32,7 +32,7 @@
 #include "net/third_party/mozilla_security_manager/nsNSSCertificateDB.h"
 #include "net/third_party/mozilla_security_manager/nsPKCS12Blob.h"
 
-#if defined(OS_CHROMEOS) || BUILDFLAG(IS_CHROMEOS_LACROS)
+#if BUILDFLAG(IS_CHROMEOS_ASH) || BUILDFLAG(IS_CHROMEOS_LACROS)
 #include "crypto/chaps_support.h"
 #endif
 

net/disk_cache/blockfile/block_files_unittest.cc

@@ -4,6 +4,7 @@
 
 #include "base/files/file_enumerator.h"
 #include "base/files/file_util.h"
+#include "build/chromeos_buildflags.h"
 #include "net/disk_cache/blockfile/block_files.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/disk_cache/disk_cache_test_base.h"
@@ -30,7 +31,7 @@ int NumberOfFiles(const base::FilePath& path) {
 namespace disk_cache {
 
 // Flaky on ChromeOS: https://crbug.com/1156795
-#if defined(OS_CHROMEOS)
+#if BUILDFLAG(IS_CHROMEOS_ASH)
 #define MAYBE_BlockFiles_Grow DISABLED_BlockFiles_Grow
 #else
 #define MAYBE_BlockFiles_Grow BlockFiles_Grow