Polish the SystemInfoProvider template code and refactor StorageInfoProvider based on it

chrome/test/data/extensions/api_test/systeminfo/storage/test_storage_api.js

Index: chrome/test/data/extensions/api_test/systeminfo/storage/test_storage_api.js
diff --git a/chrome/test/data/extensions/api_test/systeminfo/storage/test_storage_api.js b/chrome/test/data/extensions/api_test/systeminfo/storage/test_storage_api.js
index 5b4f834b3db7ee5b4d9d5f568409e52efadd7df0..787ca408abbe912b1aefdc209792a16125c5fe7b 100644
--- a/chrome/test/data/extensions/api_test/systeminfo/storage/test_storage_api.js
+++ b/chrome/test/data/extensions/api_test/systeminfo/storage/test_storage_api.js
@@ -9,8 +9,12 @@ chrome.systemInfo = chrome.experimental.systemInfo;
 chrome.test.runTests([
   function testGet() {
     chrome.systemInfo.storage.get(chrome.test.callbackPass(function(info) {
-      // TODO(hmin): Need to check the value from Mock implementation
-      chrome.test.assertTrue(info.units.length > 0);
+      chrome.test.assertTrue(info.units.length == 1);
+      var unit = info.units[0];
+      chrome.test.assertTrue(unit.id == "0xbeaf");
+      chrome.test.assertTrue(unit.type == "unknown");
+      chrome.test.assertTrue(unit.capacity == 4098);
+      chrome.test.assertTrue(unit.availableCapacity == 1024);
     }));
   }
 ]);