remoting: Use BUILDFLAG for OS checking

Use BUILDFLAG(IS_XXX) instead of defined(OS_XXX).

Generated by `os_buildflag_migration.py` (https://crrev.com/c/3311983).

[email protected]

Bug: 1234043
Test: No functionality change
Change-Id: Ida556f7dd6c846203cae3bc062da08a4d2b5fafe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3373985
Reviewed-by: Nico Weber <[email protected]>
Owners-Override: Nico Weber <[email protected]>
Commit-Queue: Xiaohan Wang <[email protected]>
Cr-Commit-Position: refs/heads/main@{#958774}
diff --git a/remoting/host/branding.h b/remoting/host/branding.h
index 575f3fb..1452803 100644
--- a/remoting/host/branding.h
+++ b/remoting/host/branding.h
@@ -10,7 +10,7 @@
 
 namespace remoting {
 
-#if defined(OS_WIN)
+#if BUILDFLAG(IS_WIN)
 // Windows chromoting service name.
 extern const wchar_t kWindowsServiceName[];
 #endif