Send UMA about requested window state from tabs API

chrome/common/extensions/api/windows.json

Index: chrome/common/extensions/api/windows.json
diff --git a/chrome/common/extensions/api/windows.json b/chrome/common/extensions/api/windows.json
index 17eb6fd896ae57299796cf2542f38149dccbdf53..3501969a01fe6b44c9c17e7b8260f89ced180756 100644
--- a/chrome/common/extensions/api/windows.json
+++ b/chrome/common/extensions/api/windows.json
@@ -17,6 +17,11 @@
         "enum": ["normal", "popup", "panel", "app", "devtools"]
       },
       {
+        // WARNING: These values are written to logs. New enum values can be\

[Mark P, 2017/03/29 20:05:40]

nit: errant \

[afakhry, 2017/03/31 03:17:29]

Done.

+        // 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.

[Mark P, 2017/03/29 20:05:40]

optional nit: move comment next to "enum": [{ line

[afakhry, 2017/03/31 03:17:29]

Done.

         "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.",