`#pragma once` for app, base, chrome, gfx, ipc, net, skia, views

BUG=50273
TEST=everything still builds, build is 10% faster on windows, same speed on mac/linux

TBR: erg

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@53716 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/net/base/dns_util.h b/net/base/dns_util.h
index f0d20516..cd81420 100644
--- a/net/base/dns_util.h
+++ b/net/base/dns_util.h
@@ -4,6 +4,7 @@
 
 #ifndef NET_BASE_DNS_UTIL_H_
 #define NET_BASE_DNS_UTIL_H_
+#pragma once
 
 #include <string>