[sensors] Add Permission guard to the generic sensor apis.

tools/metrics/rappor/rappor.xml

 <!--
 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.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome rappor metrics
 along with a detailed description for each histogram. See the design doc at
 http://www.chromium.org/developers/design-documents/rappor
@@ skipping 854 matching lines @@
 </rappor-metric>
 
 <rappor-metric name="ContentSettings.PermissionRequested.ProtectedMedia.Url2"
     type="LOW_FREQUENCY_ETLD_PLUS_ONE">
   <owner>xhwang@chromium.org</owner>
   <summary>
     The domain that issues a Protected Media Identifier permission prompt.
   </summary>
 </rappor-metric>
 
+<rappor-metric name="ContentSettings.PermissionRequested.Sensors.Url2"
+    type="LOW_FREQUENCY_ETLD_PLUS_ONE">
+  <owner>rijubrata.bhaumik@intel.com</owner>
+  <summary>
+    The domain that requests using sensor permissions.
+  </summary>
+</rappor-metric>
+
 <rappor-metric name="ContentSettings.Plugins.AddedAllowException"
     type="ETLD_PLUS_ONE">
   <owner>tommycli@chromium.org</owner>
   <summary>
     The eTLD+1 of a URL that the user added to the ALLOW site exceptions for the
     Plugins Content Setting.
   </summary>
 </rappor-metric>
 
 <rappor-metric name="CustomTabs.ServiceClient.PackageName"
@@ skipping 1574 matching lines @@
     <flag bit="1" label="IS_REPEAT_VISIT"/>
     <summary>
       Bitfield of the state from an SSL warning interstitial.
     </summary>
   </flags-field>
 </rappor-metric>
 
 </rappor-metrics>
 
 </rappor-configuration>