Expose microphone content setting to extensions.

chrome/common/extensions/api/content_settings.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": "contentSettings",
     "description": "Use the <code>chrome.contentSettings</code> API to change settings that control whether websites can use features such as cookies, JavaScript, and plug-ins. More generally speaking, content settings allow you to customize Chrome's behavior on a per-site basis instead of globally.",
     "compiler_options": {
       "generate_type_functions": true
@@ skipping 218 matching lines @@
           {"type":"string", "enum": ["allow", "block", "ask"]}
         ]
       },
       "mouselock": {
         "$ref": "ContentSetting",
         "description": "Whether to allow sites to disable the mouse cursor. One of <br><var>allow</var>: Allow sites to disable the mouse cursor,<br><var>block</var>: Don't allow sites to disable the mouse cursor,<br><var>ask</var>: Ask when a site wants to disable the mouse cursor. <br>Default is <var>ask</var>.<br>The primary URL is the URL of the top-level frame. The secondary URL is not used.",
         "value": [
           "mouselock",
           {"type":"string", "enum": ["allow", "block", "ask"]}
         ]
+      },
+      "mediaStreamMic": {

[msramek, 2015/01/30 11:57:02]

I kept the internal name here, just renamed from dash-separated to camelCase to
fit the JS style.

However, the "media stream" prefix is a result of the fact that microphone and
camera used to be a single content setting "media stream", which is now
deprecated. Do we want to keep the name for consistency, or rename it to e.g.
"microphone" (as extension developers needn't care about the original deprecated
setting)?

[Mike West, 2015/01/30 12:05:59]

Renaming for the JS interface seems pretty reasonable.

+        "$ref": "ContentSetting",
+        "description": "Whether to allow sites to access the microphone. One of <br><var>allow</var>: Allow sites to access the microphone,<br><var>block</var>: Don't allow sites to access the microphone,<br><var>ask</var>: Ask when a site wants to access the microphone. <br>Default is <var>ask</var>.<br>The primary URL is the URL of the document which requested microphone access. The secondary URL is not used.",
+        "value": [
+          "media-stream-mic",
+          {"type":"string", "enum": ["allow", "block", "ask"]}
+        ]
       }
     }
   }
 ]