Make `content` target build without unused data members on Linux.

content/browser/webui/url_data_manager_backend.cc

Index: content/browser/webui/url_data_manager_backend.cc
diff --git a/content/browser/webui/url_data_manager_backend.cc b/content/browser/webui/url_data_manager_backend.cc
index 69f0861d10d2ea4a59f0eda10e07e36a87110b9b..38ff6536f3f93be74bf2f335f4d57ceb8a8c9f61 100644
--- a/content/browser/webui/url_data_manager_backend.cc
+++ b/content/browser/webui/url_data_manager_backend.cc
@@ -491,7 +491,6 @@ class ChromeProtocolHandler
                         ChromeBlobStorageContext* blob_storage_context)
       : resource_context_(resource_context),
         is_incognito_(is_incognito),
-        appcache_service_(appcache_service),
         blob_storage_context_(blob_storage_context) {}
   ~ChromeProtocolHandler() override {}
 
@@ -551,7 +550,6 @@ class ChromeProtocolHandler
 
   // True when generated from an incognito profile.
   const bool is_incognito_;
-  AppCacheServiceImpl* appcache_service_;
   ChromeBlobStorageContext* blob_storage_context_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeProtocolHandler);