Refine systemInfo.cpu API defintions and provide systemInfo.cpu.get impl for Windows and Linux

chrome/test/data/extensions/api_test/systeminfo/cpu/test_cpuinfo_api.js

 // 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.
 
 // systeminfo.cpu api test
 // browser_tests.exe --gtest_filter=SystemInfoCpuApiTest.*
 
 chrome.systemInfo = chrome.experimental.systemInfo;
 
 chrome.test.runTests([
   function testGet() {
     for(var i = 0; i < 20; ++i) {
       chrome.systemInfo.cpu.get(chrome.test.callbackPass(function(result) {
-        chrome.test.assertTrue(result.cores.length == 4);
-        var core;
-        for (var i = 0; i < result.cores.length; ++i) {
-          core = result.cores[i];
-          chrome.test.assertTrue(core.load == i*10);
-        }
+        chrome.test.assertEq(4, result.numOfProcessors);
+        chrome.test.assertEq("x86", result.archName);
+        chrome.test.assertEq("unknown", result.modelName);
       }));
     }
   },
 ]);