[Sync] Add support for server-controlled favicon sync limit

sync/internal_api/public/util/experiments.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 SYNC_UTIL_EXPERIMENTS_
 #define SYNC_UTIL_EXPERIMENTS_
 
 #include "sync/internal_api/public/base/model_type.h"
 
 namespace syncer {
 
 const char kKeystoreEncryptionTag[] = "keystore_encryption";
 const char kKeystoreEncryptionFlag[] = "sync-keystore-encryption";
 const char kAutofillCullingTag[] = "autofill_culling";
 const char kFullHistorySyncTag[] = "history_delete_directives";
 const char kFullHistorySyncFlag[] = "full-history-sync";
 const char kFaviconSyncTag[] = "favicon_sync";
 const char kFaviconSyncFlag[] = "enable-sync-favicons";
 
 // A structure to hold the enable status of experimental sync features.
 struct Experiments {
   Experiments() : keystore_encryption(false),
                   autofill_culling(false),
                   full_history_sync(false),
-                  favicon_sync(false) {}
+                  favicon_sync(false),
+                  favicon_sync_limit(200) {}
 
   bool Matches(const Experiments& rhs) {
     return (keystore_encryption == rhs.keystore_encryption &&
             autofill_culling == rhs.autofill_culling &&
             full_history_sync == rhs.full_history_sync &&
-            favicon_sync == rhs.favicon_sync);
+            favicon_sync == rhs.favicon_sync &&
+            favicon_sync_limit == rhs.favicon_sync_limit);
   }
 
   // Enable keystore encryption logic and the new encryption UI.
   bool keystore_encryption;
 
   // Enable deletion of expired autofill entries (if autofill sync is enabled).
   bool autofill_culling;
 
   // Enable full history sync (and history delete directives) for this client.
   bool full_history_sync;
 
   // Enable the favicons sync datatypes (favicon images and favicon tracking).
   bool favicon_sync;
+
+  // The number of favicons that a client is permitted to sync.
+  int favicon_sync_limit;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_UTIL_EXPERIMENTS_