Add chrome.inputMethodPrivate.onImeMenuActivationChanged API.

chrome/common/extensions/api/input_method_private.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": "inputMethodPrivate",
     "description": "none",
     "functions": [
       {
@@ skipping 207 matching lines @@
             }
           }, {
             "name": "removed",
             "type": "array",
             "description": "List of removed words.",
             "items": {
               "type": "string"
             }
           }
         ]
+      }, {
+        "name": "onImeMenuActivationChanged",
+        "type": "function",
+        "description": "Fired when the system IME Menu is activated",

[Devlin, 2016/01/13 18:11:27]

nit: lowercase "menu"
Is this only fired when the menu is activated?  Or also when it is deactivated? 
(I think the latter, in which case this should say "Fired when the system IME
menu is activated or deactivated.")

[Azure Wei, 2016/01/14 09:38:26]

Done.

+        "parameters": [
+          {
+            "name": "activation",
+            "type": "boolean",
+            "description": "Whether the IME menu is activated or deactivated"

[Devlin, 2016/01/13 18:11:27]

nit: the phrasing here is a bit weird, because it makes it difficult to
understand whether this refers to the current state, or the state it was
transitioned out of.  Assuming it's the current state, say something like
"Whether the IME menu is currently active."

[Azure Wei, 2016/01/14 09:38:26]

Done.

+          }
+        ]
       }
     ]
   }
 ]