There are 6 more extension IDs on the list which are currently unused (but Google could add these extensions to the Web Store at any time). Apparently, the trusted extensions are currently Google +1 Button and Google+ Notifications. The list can be found in extension_webstore_private_api.cc file in the Chrome source code. First of all there is a method silentlyInstall(), the documentation claims that only some extensions can be installed this way however. It is apparently the Chrome equivalent of Gecko’s InstallTrigger, with the difference that Firefox makes InstallTrigger available to all websites. It isn’t documented online but you can find the documentation if you search in the chrome.dll file. The webstorePrivate API is (as its name already says) meant for the Web Store only. But it can do more: enable or disable extensions and even uninstall them without any kind of visible notification. The former allows querying your installed extensions which explains how the website learns about them. A look at the Preferences file shows the privileges of the Web Store app: management API and webstorePrivate API.
Web apps in Chrome can have special privileges if they request them, same as extensions. The Web Store is a pre-installed web app (actually, it is even hardcoded into the browser). How does the web page know which extensions you have installed?
One particular feature caught my attention: it marks the extensions that you already have with a check mark.
#ADBLOCK PLUS FOR CHROME INSTALL#
Google recently launched a redesigned version of its Web Store where one can install extensions and web apps. Adblock Plus and (a little) more Google Chrome and pre-installed web apps