Firstly you would have to set up a WebViewClient/WebChromeClient for your webView. You might wanna look at the WebViewClient/WebChromeClient classes respectively. There's a bunch of APIs listed under them, I've chalked out some of them which might be of interest to you: (Excerpts from Android Developer's Site)
/********WebChromeClient CLASS******/
public void getVisitedHistory (ValueCallback callback)
Obtains a list of all visited history items, used for link coloring
/*********WebStorage CLASS ****/
public void getOrigins (ValueCallback callback)
Gets the origins currently using either the Application Cache or Web SQL Database APIs. This method operates asynchronously, with the result being provided via a ValueCallback. The origins are provided as a map, of type Map, from the string representation of the origin to a WebStorage.Origin object.
If none of these seem to do the trick then you could rely on directly querying your application's cache directory (/data/data/my_app_package/cache under DDMS tab in eclipse IDE), programmatically you will be able to access the cache directory using the getCacheDir() API. Please refer to How do I view Android application specific cache? for the exact details.