Refactor prerender pending swap logic.

chrome/browser/prerender/prerender_events.h

 // Copyright (c) 2013 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 CHROME_BROWSER_PRERENDER_PRERENDER_EVENTS_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_EVENTS_H_
 
 namespace prerender {
 
 // Events registered during prerendering used for debugging purposes and to
 // gather metrics.
 enum PrerenderEvent {
   PRERENDER_EVENT_SWAPIN_NO_DELEGATE = 0,
   PRERENDER_EVENT_SWAPIN_CANDIDATE = 1,
   PRERENDER_EVENT_SWAPIN_CANDIDATE_NAMESPACE_MATCHES = 2,
   PRERENDER_EVENT_SWAPIN_NO_MERGE_PENDING = 3,
   PRERENDER_EVENT_SWAPIN_MERGING_DISABLED = 4,
   PRERENDER_EVENT_SWAPIN_ISSUING_MERGE = 5,
   PRERENDER_EVENT_MERGE_FOR_SWAPIN_CANDIDATE = 6,
   PRERENDER_EVENT_MERGE_RESULT_NO_PENDING_SWAPIN = 7,
-  PRERENDER_EVENT_MERGE_RESULT_TIMEOUT_CB = 8,
-  PRERENDER_EVENT_MERGE_RESULT_RESULT_CB = 9,
+  // Obsolete: PRERENDER_EVENT_MERGE_RESULT_TIMEOUT_CB = 8,
+  // Obsolete: PRERENDER_EVENT_MERGE_RESULT_RESULT_CB = 9,
   PRERENDER_EVENT_MERGE_RESULT_TIMED_OUT = 10,
   PRERENDER_EVENT_MERGE_RESULT_MERGE_DONE = 11,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_NAMESPACE_NOT_FOUND = 12,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_NAMESPACE_NOT_ALIAS = 13,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_NOT_LOGGING = 14,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_NO_TRANSACTIONS = 15,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_TOO_MANY_TRANSACTIONS = 16,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_NOT_MERGEABLE = 17,
   PRERENDER_EVENT_MERGE_RESULT_RESULT_MERGEABLE = 18,
   PRERENDER_EVENT_MERGE_RESULT_MERGE_FAILED = 19,
   PRERENDER_EVENT_MERGE_RESULT_SWAPPING_IN = 20,
-  PRERENDER_EVENT_MERGE_RESULT_SWAPIN_SUCCESSFUL = 21,
+  // Obsolete: PRERENDER_EVENT_MERGE_RESULT_SWAPIN_SUCCESSFUL = 21,
   PRERENDER_EVENT_MERGE_RESULT_SWAPIN_FAILED = 22,
   PRERENDER_EVENT_MAX,
 };
 
 // Return a human-readable name for |event|.
 const char* NameFromPrerenderEvent(PrerenderEvent event);
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_EVENTS_H_