Update MimeSniffingResourceHandler tests to use MockResourceLoader.

content/browser/loader/resource_controller.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.
 
 #ifndef CONTENT_BROWSER_LOADER_RESOURCE_CONTROLLER_H_
 #define CONTENT_BROWSER_LOADER_RESOURCE_CONTROLLER_H_
 
 #include "content/common/content_export.h"
 
 namespace content {
 
 // Used to either resume a deferred resource load or cancel a resource load at
 // any time.  CancelAndIgnore is a variation of Cancel that also causes the
 // requester of the resource to act like the request was never made.  By
 // default, load is cancelled with ERR_ABORTED code. CancelWithError can be used
 // to cancel load with any other error code.
 class CONTENT_EXPORT ResourceController {
  public:
   virtual void Cancel() = 0;
   virtual void CancelAndIgnore() = 0;
   virtual void CancelWithError(int error_code) = 0;
+
+  // Resumes the request. May only be called if the request was previously
+  // deferred. Guaranteed not to call back into the ResourceHandler, or destroy
+  // it, synchronously.
   virtual void Resume() = 0;
 
  protected:
   virtual ~ResourceController() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LOADER_RESOURCE_CONTROLLER_H_