Added new methods to IWebCoreStatistics

    To better support memory leak testing, I've added the following methods:
    - resourceCacheImageCount
    - resourceCacheCSSCount
    - resourceCacheScriptCount
    - resourceCacheFontCount
    - jsHeapUsageKB
    - docCount
    - frameCount
    - nodeCount
    - jsListenerCount
Re-implemented text input mouse click handler

Instead of making the callback from the event handler, the text input
mouse click delegate is now invoked from the default event handler in
HTMLTextFormControlElement (which covers text inputs and text areas).
Earlier changes to EventHandler are reverted in this change.