Update FeatureObserver on top level navigation in addition to page destruction.
https://bugs.webkit.org/show_bug.cgi?id=109874

Patch by Kassy Coan <kassycoan@chromium.org> on 2013-02-19
Reviewed by Adam Barth.

No new tests. Only effect is to histogram more frequently.

* loader/FrameLoader.cpp:
(WebCore::FrameLoader::dispatchDidCommitLoad):
* page/FeatureObserver.cpp:
(WebCore::FeatureObserver::~FeatureObserver):
(WebCore):
(WebCore::FeatureObserver::updateMeasurements):
(WebCore::FeatureObserver::didCommitLoad):
* page/FeatureObserver.h:
(FeatureObserver):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143363 268f45cc-cd09-0410-ab3c-d52691b4dbfc