Raise the chrome.storage.sync per-item quota to 8K.

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 163 matching lines @@
       "sync": {
         "$ref": "StorageArea",
         "description": "Items in the <code>sync</code> storage area are synced using Chrome Sync.",
         "value": [ "sync" ],
         "properties": {
           "QUOTA_BYTES": {
             "value": 102400,
             "description": "The maximum total amount (in bytes) of data that can be stored in sync storage, as measured by the JSON stringification of every value plus every key's length. Updates that would cause this limit to be exceeded fail immediately and set $(ref:runtime.lastError)."
           },
           "QUOTA_BYTES_PER_ITEM": {
-            "value": 4096,
+            "value": 8192,
             "description": "The maximum size (in bytes) of each individual item in sync storage, as measured by the JSON stringification of its value plus its key length. Updates containing items larger than this limit will fail immediately and set $(ref:runtime.lastError)."
           },
           "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 $(ref:runtime.lastError)."
           },
@@ skipping 15 matching lines @@
         }
       },
       "managed": {
         "$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" ]
       }
     }
   }
 ]