Added caching for the next change id.
Added caching for the next change id.

Change retrievals from Drive are no longer duplicated across multiple runs.
liqingzhu/mobile-chrome-apps,guozanhua/mobile-chrome-apps,wudkj/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,hgl888/mobile-chrome-apps,wudkj/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,guozanhua/mobile-chrome-apps,hgl888/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,guozanhua/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,wudkj/mobile-chrome-apps,wudkj/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,chirilo/mobile-chrome-apps,chirilo/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,chirilo/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,hgl888/mobile-chrome-apps,guozanhua/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,chirilo/mobile-chrome-apps