AppCache: Remove unused superclass from AppCacheRequestHandler.

The base::SupportsUserData::Data superclass seems to be left over from a
previous architecture. It adds cognitive overhead, as it implies that
AppCacheRequestHandler may be used in a base::SupportsUserData
container.

Change-Id: Ibe61b6cec71ebd513eb8ccd896845d4c04b47f6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2066104
Commit-Queue: Joshua Bell <jsbell@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743199}

content/browser/appcache/appcache_request_handler.h

@@ -12,7 +12,6 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/supports_user_data.h"
 #include "content/browser/appcache/appcache_entry.h"
 #include "content/browser/appcache/appcache_host.h"
 #include "content/browser/appcache/appcache_request_handler.h"
@@ -44,8 +43,7 @@ class AppCacheHost;
 // should use AppCacheHost::CreateRequestHandler to manufacture instances
 // that can retrieve resources for a particular host.
 class CONTENT_EXPORT AppCacheRequestHandler
-    : public base::SupportsUserData::Data,
-      public AppCacheHost::Observer,
+    : public AppCacheHost::Observer,
       public AppCacheServiceImpl::Observer,
       public AppCacheStorage::Delegate,
       public NavigationLoaderInterceptor {