Added documentation for In-App Payments API.

chrome/common/extensions/api/_permission_features.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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "activeTab": {
     "channel": "stable",
@@ skipping 271 matching lines @@
     "channel": "stable",
     "extension_types": [
       "packaged_app"
     ],
     "location": "component"
   },
   "idle": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app", "platform_app"]
   },
+  "inAppPayments": {
+    "channel": "dev",
+    "extension_types": ["platform_app"]
+  },

[not at google - send to devlin, 2013/07/08 16:15:43]

things in chrome/common/extensions/api are only for actual chrome APIs, which
this isn't. I'll comment on the public html file with something that should
work, or should at least not require much extra effort to make work.

[Andy, 2013/07/09 00:51:23]

Done.

   "input": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"],
     "inplies_full_url_access": true
   },
   "inputMethodPrivate": [{
     "channel": "stable",
     "extension_types": ["extension", "packaged_app", "platform_app"],
     "whitelist": [
       "haiffjcadagjlijoggckpgfnoeiflnem",  // Citrix Receiver
@@ skipping 338 matching lines @@
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"]
   },
   "webview": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   }
 }