Rename FeatureObserver to UseCounter to make clear that all it stores are usage counts.

Source/WebCore/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer. 
@@ skipping 532 matching lines @@
             return;
         }
     }
 
     ASSERT(!mainResourceLoader() || !mainResourceLoader()->defersLoading());
 
     if (m_isLoadingMultipartContent) {
         setupForReplace();
         m_mainResource->clear();
     } else if (response.isMultipart()) {
-        FeatureObserver::observe(m_frame->document(), FeatureObserver::MultipartMainResource);
+        UseCounter::observe(m_frame->document(), UseCounter::MultipartMainResource);
         m_isLoadingMultipartContent = true;
     }
 
     m_response = response;
 
     if (m_identifierForLoadWithoutResourceLoader)
         frameLoader()->notifier()->dispatchDidReceiveResponse(this, m_identifierForLoadWithoutResourceLoader, m_response, 0);
 
     ASSERT(!m_waitingForContentPolicy);
     m_waitingForContentPolicy = true;
@@ skipping 638 matching lines @@
     commitLoad(resourceData->data(), resourceData->size());
 }
 
 void DocumentLoader::handledOnloadEvents()
 {
     m_wasOnloadHandled = true;
     applicationCacheHost()->stopDeferringEvents();
 }
 
 } // namespace WebCore