Prevent unnecessary prompts when unpacked extensions use chrome.permissions.request.

chrome/test/data/extensions/api_test/permissions/optional_deny/background.js

 // Copyright (c) 2011 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.
 
 var assertFalse = chrome.test.assertFalse;
 var assertTrue = chrome.test.assertTrue;
 var pass = chrome.test.callbackPass;
 
 var NO_TABS_PERMISSION =
     "You do not have permission to use 'windows.getAll'.";
@@ skipping 42 matching lines @@
                 chrome.test.fail("Should not have tabs API permission.");
               });
             } catch (e) {
               assertTrue(e.message.indexOf(NO_TABS_PERMISSION) == 0);
             }
 
             doReq('http://b.c.com/', pass(function(result) {
               assertFalse(result);
             }));
       }));
+    },
+
+    function noPromptForActivePermissions() {
+      // We shouldn't prompt if the extension already has the permissions.
+      chrome.permissions.request(
+          {permissions: ["management"]},
+          pass(function(granted) {
+        assertTrue(granted);
+      }));
     }
   ]);
 });