Define the storage API throttling constants in storage.json so that they are

chrome/common/extensions/api/storage.json

 // 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.
 
 [
   {
     "namespace": "storage",
     "unprivileged": true,
     "types": [
       {
@@ skipping 167 matching lines @@
             "value": 102400,
             "description": "The maximum total amount (in bytes) of data that can be stored in sync storage."
           },
           "QUOTA_BYTES_PER_ITEM": {
             "value": 2048,
             "description": "The maximum size (in bytes) of each individual item in sync storage."
           },
           "MAX_ITEMS": {
             "value": 512,
             "description": "The maximum number of items that can be stored in sync storage."
+          },
+          "MAX_WRITE_OPERATIONS_PER_HOUR": {
+            "value": 1000,
+            "description": "The maximum number of <code>set</code>, <code>remove</code>, or <code>clear</code> operations that can be performed each hour."
+          },
+          "MAX_SUSTAINED_WRITE_OPERATIONS_PER_MINUTE": {
+            "value": 10,
+            "description": "The maximum number of <code>set</code>, <code>remove</code>, or <code>clear</code> operations that can be performed each minute, sustained over 10 minutes."
           }
         }
       },
       "local": {
         "$ref": "StorageArea",
         "description": "Items under the \"local\" namespace are local to each machine.",
         "value": [ "local" ],
         "properties": {
           "QUOTA_BYTES": {
             "value": 5242880,
             "description": "The maximum amount (in bytes) of data that can be stored in local storage. This value will be ignored if the extension has the <code>unlimitedStorage</code> permission."
           }
         }
       }
     }
   }
 ]