Refactor prerender pending swap logic.

chrome/browser/prerender/prerender_events.h

Index: chrome/browser/prerender/prerender_events.h
diff --git a/chrome/browser/prerender/prerender_events.h b/chrome/browser/prerender/prerender_events.h
index d1df846dedf5e564a249df12da55358971538a47..93af72ca80ff94a4d444b4585f69583ee1973f22 100644
--- a/chrome/browser/prerender/prerender_events.h
+++ b/chrome/browser/prerender/prerender_events.h
@@ -18,8 +18,8 @@ enum PrerenderEvent {
   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,
@@ -31,7 +31,7 @@ enum PrerenderEvent {
   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,
 };