Add sanbdoxed_pages to allow extension/app pages to be served in a sandboxed, unique origin

chrome/common/extensions/extension_constants.h

Index: chrome/common/extensions/extension_constants.h
diff --git a/chrome/common/extensions/extension_constants.h b/chrome/common/extensions/extension_constants.h
index 7b3143de13273b79a9b2f26a9932722d79412ccf..ba850ccb49d1597ce5a09a9326357564087d29aa 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -252,6 +252,10 @@ namespace extension_misc {
   // Error indicating that the app notifications API is not accessible by split
   // mode extensions in incognito windows.
   extern const char kAppNotificationsIncognitoError[];
+
+  // CSP value that makes resources be sandboxed (served from an unique origin,
+  // top-level navigation and popups are disabled).
+  extern const char kSandboxedContentSecurityPolicy[];
 }  // extension_misc
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_