PDF: Add UMA to track embedded PDF triggered drive-by downloads.

content/public/browser/download_manager_delegate.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_PUBLIC_BROWSER_DOWNLOAD_MANAGER_DELEGATE_H_
 #define CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_DELEGATE_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 146 matching lines @@
       const CheckForFileExistenceCallback& callback) {}
 
   // Return a GUID string used for identifying the application to the system AV
   // function for scanning downloaded files. If no GUID is provided or if the
   // provided GUID is invalid, then the appropriate quarantining will be
   // performed manually without passing the download to the system AV function.
   //
   // This GUID is only used on Windows.
   virtual std::string ApplicationClientIdForFileScanning() const;
 
+  // Records metrics about a drive-by PDF download.
+  virtual void RecordDriveByPDFDownload() const {}
+
  protected:
   virtual ~DownloadManagerDelegate();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_DELEGATE_H_