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

Source/bindings/scripts/CodeGeneratorV8.pm

Index: Source/bindings/scripts/CodeGeneratorV8.pm
diff --git a/Source/bindings/scripts/CodeGeneratorV8.pm b/Source/bindings/scripts/CodeGeneratorV8.pm
index b01b603d2f88d21588195f79729e55f12cd9023b..0f3cfb3aa870ecc4187240fd6830428aa9d925ad 100644
--- a/Source/bindings/scripts/CodeGeneratorV8.pm
+++ b/Source/bindings/scripts/CodeGeneratorV8.pm
@@ -911,8 +911,8 @@ sub GenerateFeatureObservation
     my $measureAs = shift;
 
     if ($measureAs) {
-        AddToImplIncludes("FeatureObserver.h");
-        return "    FeatureObserver::observe(activeDOMWindow(BindingState::instance()), FeatureObserver::${measureAs});\n";
+        AddToImplIncludes("UseCounter.h");
+        return "    UseCounter::observe(activeDOMWindow(BindingState::instance()), UseCounter::${measureAs});\n";
     }
 
     return "";