Make classes and structures in core/dom fast-allocated.

Source/core/dom/Microtask.h

Index: Source/core/dom/Microtask.h
diff --git a/Source/core/dom/Microtask.h b/Source/core/dom/Microtask.h
index e111c03da1dac1d1b06913a2c62c37b97c434e99..97f077117aaac848048c337cb43f4046cd474626 100644
--- a/Source/core/dom/Microtask.h
+++ b/Source/core/dom/Microtask.h
@@ -34,6 +34,7 @@
 #include "bindings/core/v8/ScriptState.h"
 #include "core/CoreExport.h"
 #include "public/platform/WebThread.h"
+#include "wtf/Allocator.h"
 #include "wtf/Functional.h"
 #include "wtf/PassOwnPtr.h"
 #include <v8.h>
@@ -41,6 +42,7 @@
 namespace blink {
 
 class CORE_EXPORT Microtask {
+    STATIC_ONLY(Microtask);
 public:
     static void performCheckpoint(v8::Isolate*);
     static bool performingCheckpoint(v8::Isolate*);
@@ -50,9 +52,6 @@ public:
     // ScriptState themselves.
     static void enqueueMicrotask(PassOwnPtr<WebThread::Task>);
     static void enqueueMicrotask(PassOwnPtr<Closure>);
-
-private:
-    explicit Microtask();
 };
 
 } // namespace blink