CrNet: add pauseable NSURLProtocol and switch to using it

ios/net/crn_http_protocol_handler_proxy.h

 // Copyright 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.
 
 #ifndef IOS_NET_CRN_HTTP_PROTOCOL_HANDLER_PROXY_H_
 #define IOS_NET_CRN_HTTP_PROTOCOL_HANDLER_PROXY_H_
 
 #import <Foundation/Foundation.h>
 
 #import "ios/net/clients/crn_network_client_protocol.h"
 
 // HttpProtocolHandlerProxy is responsible for managing access to the
 // NSURLProtocol and its client.
 @protocol CRNHTTPProtocolHandlerProxy<CRNNetworkClientProtocol>
 
 // Invalidates any reference to the protocol handler: the handler will never
 // be called after this.
 // Called from the client thread.

[droger, 2015/06/11 08:56:19]

Maybe remove this "Called from the client thread." and add a comment for the
whole class saying that:
- methods inherited from CRNNetworkClientProtocol can be called from any thread
(but all on the same)
- the other methods must be called on the client thread.

[droger, 2015/06/11 08:58:36]

Actually I'm not sure if all the methods of CRNNetworkClientProtocol have to be
called from the same thread or not. For sure there aren't any checks that they
indeed are.

[droger, 2015/06/11 09:01:21]

Looking at the code I would think that in practice they are all called from the
same thread, and other CRNNetworkClientProtocol have DCHECKs for that (see for
example CRNForwardingNetworkClient).
Digging into this may be out of scope of your work though.

[Elly Fong-Jones, 2015/06/11 13:49:33]

Documented, at least.

 - (void)invalidate;
 
+// Pauses notifications from this protocol handler.
+- (void)pause;
+
+// Resumes notifications from this protocol handler.
+- (void)resume;
+
 @end
 
 #endif  // IOS_NET_CRN_HTTP_PROTOCOL_HANDLER_PROXY_H_