Add histogram for Blink's spell check request interval

third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 105 matching lines @@
   void ClearProcessingRequest();
 
   Member<LocalFrame> frame_;
   LocalFrame& GetFrame() const {
     DCHECK(frame_);
     return *frame_;
   }
 
   int last_request_sequence_;
   int last_processed_sequence_;
+  double last_request_time_;
 
   TaskRunnerTimer<SpellCheckRequester> timer_to_process_queued_request_;
 
   Member<SpellCheckRequest> processing_request_;
 
   typedef HeapDeque<Member<SpellCheckRequest>> RequestQueue;
   RequestQueue request_queue_;
 };
 
 }  // namespace blink
 
 #endif  // SpellCheckRequester_h