Add missing includes of //base/observer_list.h

Bug: 1290552
Change-Id: Iaee69fb002eaea3378c5082de8d847178766c412
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3544209
Reviewed-by: Lei Zhang <[email protected]>
Owners-Override: Lei Zhang <[email protected]>
Commit-Queue: David Sanders <[email protected]>
Cr-Commit-Position: refs/heads/main@{#984157}
diff --git a/net/proxy_resolution/proxy_config_service_linux.cc b/net/proxy_resolution/proxy_config_service_linux.cc
index a506b3b..ecde7a5 100644
--- a/net/proxy_resolution/proxy_config_service_linux.cc
+++ b/net/proxy_resolution/proxy_config_service_linux.cc
@@ -21,6 +21,7 @@
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/nix/xdg_util.h"
+#include "base/observer_list.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_tokenizer.h"
 #include "base/strings/string_util.h"