[SystemInfo API] Update systemInfo.storage API StorageUnitInfo Definition.

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 42d6b53e56ebf6743bbb6b595c22f9a7b9ca0db5..d4546cd0e3eab48a43c16f745dff876be701194c 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
@@ -25,9 +25,6 @@ chrome.test.runTests([
         chrome.test.assertEq(testData[i].name, units[i].name);
         chrome.test.assertEq(testData[i].type, units[i].type);
         chrome.test.assertEq(testData[i].capacity, units[i].capacity);
-        chrome.test.assertEq(testData[i].availableCapacity,
-                             units[i].availableCapacity);
-        testData[i].availableCapacity += testData[i].step;
       }
     }));
   },
@@ -38,11 +35,10 @@ chrome.test.runTests([
       function listener(changeInfo) {
         for (var i = 0; i < testData.length; ++i) {
           if (changeInfo.id == testData[i].id) {
-            // Increase its availableCapacity since it will be queried before
-            // triggering onChanged event.
-            testData[i].availableCapacity += testData[i].step;
             chrome.test.assertEq(testData[i].availableCapacity,
-                                  changeInfo.availableCapacity);
+                                 changeInfo.availableCapacity);
+            // Increase its availableCapacity with a fixed |change_step|.
+            testData[i].availableCapacity += testData[i].step;
             break;
           }
         }