Remove the extension QuotaService::SustainedLimit and its last client, the

extensions/common/api/storage.json

 // Copyright 2014 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",
     "description": "Use the <code>chrome.storage</code> API to store, retrieve, and track changes to user data.",
     "unprivileged": true,
     "types": [
@@ skipping 175 matching lines @@
           },
           "MAX_ITEMS": {
             "value": 512,
             "description": "The maximum number of items that can be stored in sync storage. Updates that would cause this limit to be exceeded will fail immediately and set $(ref:runtime.lastError)."
           },
           "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. Updates that would cause this limit to be exceeded fail immediately and set $(ref:runtime.lastError)."
           },
           "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. Updates that would cause this limit to be exceeded fail immediately and set $(ref:runtime.lastError)."
+            "value": 1000000,
+            "deprecated": "The storage.sync API no longer has a sustained write operation quota.",
+            "description": ""
           }
         }
       },
       "local": {
         "$ref": "StorageArea",
         "description": "Items in the <code>local</code> storage area 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, as measured by the JSON stringification of every value plus every key's length. This value will be ignored if the extension has the <code>unlimitedStorage</code> permission. Updates that would cause this limit to be exceeded fail immediately and set $(ref:runtime.lastError)."
           }
         }
       },
       "managed": {
         "$ref": "StorageArea",
         "description": "Items in the <code>managed</code> storage area are set by the domain administrator, and are read-only for the extension; trying to modify this namespace results in an error.",
         "value": [ "managed" ]
       }
     }
   }
 ]