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

Source/WebCore/workers/Worker.cpp

Index: Source/WebCore/workers/Worker.cpp
diff --git a/Source/WebCore/workers/Worker.cpp b/Source/WebCore/workers/Worker.cpp
index 4a8f426c9aeb250a5a91435e5c95f5ee5371b1c5..dc6be3acb186dafcca9887c4764be427597abdd6 100644
--- a/Source/WebCore/workers/Worker.cpp
+++ b/Source/WebCore/workers/Worker.cpp
@@ -36,7 +36,7 @@
 #include "EventListener.h"
 #include "EventNames.h"
 #include "ExceptionCode.h"
-#include "FeatureObserver.h"
+#include "UseCounter.h"
 #include "Frame.h"
 #include "FrameLoader.h"
 #include "InspectorInstrumentation.h"
@@ -58,7 +58,7 @@ inline Worker::Worker(ScriptExecutionContext* context)
 PassRefPtr<Worker> Worker::create(ScriptExecutionContext* context, const String& url, ExceptionCode& ec)
 {
     ASSERT(isMainThread());
-    FeatureObserver::observe(static_cast<Document*>(context)->domWindow(), FeatureObserver::WorkerStart);
+    UseCounter::observe(static_cast<Document*>(context)->domWindow(), UseCounter::WorkerStart);
 
     RefPtr<Worker> worker = adoptRef(new Worker(context));