`#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/chrome/browser/notifications/balloon_collection_impl.h b/chrome/browser/notifications/balloon_collection_impl.h
index cb06230..d1307355 100644
--- a/chrome/browser/notifications/balloon_collection_impl.h
+++ b/chrome/browser/notifications/balloon_collection_impl.h
@@ -6,6 +6,7 @@
 
 #ifndef CHROME_BROWSER_NOTIFICATIONS_BALLOON_COLLECTION_IMPL_H_
 #define CHROME_BROWSER_NOTIFICATIONS_BALLOON_COLLECTION_IMPL_H_
+#pragma once
 
 #include <deque>