Add the basic code skeleton for system info event router

chrome/common/extensions/api/experimental_system_info_storage.idl

Index: chrome/common/extensions/api/experimental_system_info_storage.idl
diff --git a/chrome/common/extensions/api/experimental_system_info_storage.idl b/chrome/common/extensions/api/experimental_system_info_storage.idl
index f56d598b12f27a904f84c3f40261b6f37ba7cf17..22d2d537ea2035d124a53f35ecc5ac64a3d7bf97 100644
--- a/chrome/common/extensions/api/experimental_system_info_storage.idl
+++ b/chrome/common/extensions/api/experimental_system_info_storage.idl
@@ -25,6 +25,13 @@ namespace experimental.systemInfo.storage {
     double availableCapacity;
   };
 
+  dictionary StorageChangeInfo {
+    // The uniue id of the storage unit already changed.
+    DOMString id;
+    // The new value of the available capacity.
+    double availableCapacity;
+  };
+
   dictionary StorageInfo {
     // The array of storage units connected to the system.
     StorageUnitInfo[] units;
@@ -36,5 +43,12 @@ namespace experimental.systemInfo.storage {
     // Get the storage information from the system.
     static void get(StorageInfoCallback callback);
   };
+
+  interface Events {
+    // Fired when the storage information is updated.
+    // |info|   : The changed information for the specified storage unit
+    static void onAvailableCapacityChanged(StorageChangeInfo info);
+  };
+ 
 };