chrome.settingsPrivate: Basic stub implementation

chrome/common/extensions/api/settings_private.json

+// Copyright 2015 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": "settingsPrivate",
+    "description": "none",
+    "platforms": ["chromeos", "win", "mac", "linux"],
+    "properties": {
+    },
+    "functions": [
+      {
+        "name": "setBooleanPref",
+        "description": "Sets a boolean settings value.",
+        "parameters": [
+          {
+            "name": "name",
+            "type": "string"
+          },
+          {
+            "name": "value",
+            "type": "boolean"
+          }
+        ]
+      },
+      {
+        "name": "setNumericPref",
+        "description": "Sets a number settings value.",
+        "parameters": [
+          {
+            "name": "name",
+            "type": "string"
+          },
+          {
+            "name": "value",
+            "type": "number"
+          }
+        ]
+      },
+      {
+        "name": "setStringPref",
+        "description": "Sets a string settings value.",
+        "parameters": [
+          {
+            "name": "name",
+            "type": "string"
+          },
+          {
+            "name": "value",
+            "type": "string"
+          }
+        ]
+      },
+      {
+        "name": "getAllPrefs",
+        "description": "Gets all the prefs in one dictionary.",

[stevenjb, 2015/03/18 00:01:04]

I think that rather than return an Object, the callback should return something
like Array<PrefEntry>, where PrefEntry is an object with a key property, and
optional string/bool/numberValue properties.

+        "parameters": []
+      }
+    ]
+  }
+]