Move session service and supervised users to buildflags.

chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc

Index: chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
diff --git a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
index e1c98e006002dcbb4c1c846aad12aacfd73a9d77..3b85089e0a469fa0277e0189c91ee545a577c392 100644
--- a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
+++ b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
@@ -91,7 +91,7 @@
 #include "extensions/common/user_script.h"
 #endif
 
-#if defined(ENABLE_SUPERVISED_USERS)
+#if BUILDFLAG(ENABLE_SUPERVISED_USERS)
 #include "chrome/browser/supervised_user/supervised_user_resource_throttle.h"
 #endif
 
@@ -618,7 +618,7 @@ void ChromeResourceDispatcherHostDelegate::AppendStandardResourceThrottles(
   if (first_throttle)
     throttles->push_back(first_throttle);
 
-#if defined(ENABLE_SUPERVISED_USERS)
+#if BUILDFLAG(ENABLE_SUPERVISED_USERS)
   bool is_subresource_request =
       resource_type != content::RESOURCE_TYPE_MAIN_FRAME;
   throttles->push_back(new SupervisedUserResourceThrottle(