Call the DidStartLoading/DidStopLoading methods on the WebViewDelegate interf...

Call the DidStartLoading/DidStopLoading methods on the WebViewDelegate interface whenever we receive the initial response for a byte range request and when the request eventually completes.

This ensures that the throbber continues to spin when these requests take a while. 

It stops spinning during load when the document load is cancelled by the plugin process. This occurs when the plugin invokes NPN_RequestRead the first time on the stream.

This fixes http://code.google.com/p/chromium/issues/detail?id=7375

Bug=7375
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=9732

[jam, 2009-02-12 23:45:25]

lgtm