AppCache: Use WeakPtr<> to fix a potential uaf bug.

content/browser/appcache/appcache_dispatcher_host.h

Index: content/browser/appcache/appcache_dispatcher_host.h
diff --git a/content/browser/appcache/appcache_dispatcher_host.h b/content/browser/appcache/appcache_dispatcher_host.h
index 30d2f86f71c822182b8d1e1aab400f0ec6a71b4f..f8909a88125a49ffc17087eac6727398e4485890 100644
--- a/content/browser/appcache/appcache_dispatcher_host.h
+++ b/content/browser/appcache/appcache_dispatcher_host.h
@@ -9,6 +9,7 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
 #include "base/process/process.h"
 #include "content/browser/appcache/appcache_backend_impl.h"
 #include "content/browser/appcache/appcache_frontend_proxy.h"
@@ -69,6 +70,8 @@ class AppCacheDispatcherHost : public BrowserMessageFilter {
   // The corresponding ChildProcessHost object's id().
   int process_id_;
 
+  base::WeakPtrFactory<AppCacheDispatcherHost> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(AppCacheDispatcherHost);
 };