Move app_host target from c/b/extensions into src/apps.

apps/app_host/update.h

Index: apps/app_host/update.h
diff --git a/chrome/browser/extensions/app_host/update.h b/apps/app_host/update.h
similarity index 70%
rename from chrome/browser/extensions/app_host/update.h
rename to apps/app_host/update.h
index af14da2753afb4bcd06886ec0965b106568c05fc..b72c985f3616f09912ce0329801d79f2c79b5d34 100644
--- a/chrome/browser/extensions/app_host/update.h
+++ b/apps/app_host/update.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROME_BROWSER_EXTENSIONS_APP_HOST_UPDATE_H_
-#define CHROME_BROWSER_EXTENSIONS_APP_HOST_UPDATE_H_
+#ifndef APPS_APP_HOST_UPDATE_H_
+#define APPS_APP_HOST_UPDATE_H_
 
 namespace app_host {
 
@@ -13,4 +13,4 @@ void EnsureAppHostUpToDate();
 
 }  // namespace app_host
 
-#endif  // CHROME_BROWSER_EXTENSIONS_APP_HOST_UPDATE_H_
+#endif  // APPS_APP_HOST_UPDATE_H_