Send UMA about requested window state from tabs API

chrome/common/extensions/api/windows.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": "windows",
     "description": "Use the <code>chrome.windows</code> API to interact with browser windows. You can use this API to create, modify, and rearrange windows in the browser.",
     "compiler_options": {
       "implemented_in": "chrome/browser/extensions/api/tabs/tabs_api.h"
     },
     "types": [
       {
         "id": "WindowType",
         "type": "string",
         "description": "The type of browser window this is. Under some circumstances a Window may not be assigned type property, for example when querying closed windows from the $(ref:sessions) API.",
         "enum": ["normal", "popup", "panel", "app", "devtools"]
       },
       {
         "id": "WindowState",
         "type": "string",
         "description": "The state of this browser window. Under some circumstances a Window may not be assigned state property, for example when querying closed windows from the $(ref:sessions) API.",
+        // WARNING: These values are written to logs. New enum values can be
+        // added, but existing enums must never be renumbered or deleted and
+        // reused. If something needs to be removed, make sure to remove the
+        // "TabsApi.RequestedWindowState" histogram as it will be no longer
+        // valid, and make sure to mark it as obsolete in histograms.xml.
         "enum": [{
           "name": "normal",
           "description": "Normal window state (i.e. not minimized, maximized, or fullscreen)."
         }, {
           "name": "minimized",
           "description": "Minimized window state."
         }, {
           "name": "maximized",
           "description": "Maximized window state."
         }, {
@@ skipping 297 matching lines @@
             "description": "Conditions that the window's type being removed must satisfy. By default it will satisfy <code>['app', 'normal', 'panel', 'popup']</code>, with <code>'app'</code> and <code>'panel'</code> window types limited to the extension's own windows."
           }
         ],
         "parameters": [
           {"type": "integer", "name": "windowId", "minimum": -1, "description": "ID of the newly focused window."}
         ]
       }
     ]
   }
 ]