[Offline Pages] Adds event logs for requests dropped due to number of start or complete attempts.

components/offline_pages/background/offliner.h

 // Copyright 2016 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 COMPONENTS_OFFLINE_PAGES_BACKGROUND_OFFLINER_H_
 #define COMPONENTS_OFFLINE_PAGES_BACKGROUND_OFFLINER_H_
 
 #include <string>
 
 #include "base/callback.h"
 
 namespace offline_pages {
 
 class SavePageRequest;
 
 // Interface of a class responsible for constructing an offline page given
 // a request with a URL.
 class Offliner {
  public:
   // Status of processing an offline page request.
   // WARNING: You must update histograms.xml to match any changes made to
   // this enum (ie, OfflinePagesBackgroundOfflinerRequestStatus histogram enum).
+  // Also update related switch code in RequestCoordinatorEventLogger.
   enum RequestStatus {
     // No status determined/reported yet. Interim status, not sent in callback.
     UNKNOWN = 0,
     // Page loaded but not (yet) saved. Interim status, not sent in callback.
     LOADED = 1,
     // Offline page snapshot saved.
     SAVED = 2,
     // RequestCoordinator canceled request.
     REQUEST_COORDINATOR_CANCELED = 3,
     // Prerendering was canceled.
@@ skipping 26 matching lines @@
   // Clears the currently processing request, if any, and skips running its
   // CompletionCallback.
   virtual void Cancel() = 0;
 
   // TODO(dougarnett): add policy support methods.
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_BACKGROUND_OFFLINER_H_