Revert a workaround commit for a UAF crash.

net/url_request/url_request_context.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This class represents contextual information (cookies, cache, etc.)
 // that's useful when processing resource requests.
 // The class is reference-counted so that it can be cleaned up after any
 // requests that are using it have been completed.
 
 #ifndef NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_
@@ skipping 27 matching lines @@
 class ProxyService;
 class URLRequest;
 class URLRequestJobFactory;
 class URLRequestThrottlerManager;
 
 // Subclass to provide application-specific context for URLRequest
 // instances. Note that URLRequestContext typically does not provide storage for
 // these member variables, since they may be shared. For the ones that aren't
 // shared, URLRequestContextStorage can be helpful in defining their storage.
 class NET_EXPORT URLRequestContext
-    : NON_EXPORTED_BASE(public base::NonThreadSafe),
-      public base::SupportsWeakPtr<URLRequestContext> {
+    : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
   URLRequestContext();
   virtual ~URLRequestContext();
 
   // Copies the state from |other| into this context.
   void CopyFrom(const URLRequestContext* other);
 
   // May return NULL if this context doesn't have an associated network session.
   const HttpNetworkSession::Params* GetNetworkSessionParams() const;
 
@@ skipping 171 matching lines @@
   // ---------------------------------------------------------------------------
 
   scoped_ptr<std::set<const URLRequest*> > url_requests_;
 
   DISALLOW_COPY_AND_ASSIGN(URLRequestContext);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_