[Extension Doc]Declare Permissions and Warn Users

This doc is an attempt to consolidate spread out information on permissions.
It asks developers to make features that rely on permissions with warnings
optional, therefore making those permissions optional.
Includes tables of different types of permissions.

Bug: None
Change-Id: I1f0cc3934d676f16854c2725a33738916879efa2
Reviewed-on: https://chromium-review.googlesource.com/914866
Commit-Queue: Crystal Lambert <crystallambert@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557900}

chrome/common/extensions/docs/templates/json/chrome_sidenav.json

@@ -35,6 +35,10 @@
                 "title": "Design User Interface",
                 "href": "/extensions/user_interface"
               },
+              {
+                "title": "Declare Permissions and Warn Users",
+                "href": "/extensions/permission_warnings"
+              },
               {
                 "title": "Reach Peak Performance",
                 "href": "/extensions/performance"
@@ -47,10 +51,6 @@
                 "title": "Stay Secure",
                 "href": "/extensions/security"
               },
-              {
-                "title": "activeTab Permission",
-                "href": "/extensions/activeTab"
-              },
               {
                 "title": "OAuth",
                 "href": "/extensions/tut_oauth"