Limit stack-allocated uses of CancellableTaskFactory(PassOwnPtr<Closure>).

Source/platform/scheduler/CancellableTaskFactory.h

Index: Source/platform/scheduler/CancellableTaskFactory.h
diff --git a/Source/platform/scheduler/CancellableTaskFactory.h b/Source/platform/scheduler/CancellableTaskFactory.h
index 932963a6d452b8496c09f94c4e29110396474339..dc378d3a4927a7e3bfa55892313a1d67e2f64704 100644
--- a/Source/platform/scheduler/CancellableTaskFactory.h
+++ b/Source/platform/scheduler/CancellableTaskFactory.h
@@ -48,13 +48,6 @@ public:
         return adoptPtr(new CancellableTaskFactory(WTF::bind(method, thisObject)));
     }
 
-    // Only intended used by unit tests. Please use leak safe create() factory method, if possible.
-    explicit CancellableTaskFactory(PassOwnPtr<Closure> closure)
-        : m_closure(closure)
-        , m_weakPtrFactory(this)
-    {
-    }
-
     bool isPending() const
     {
         return m_weakPtrFactory.hasWeakPtrs();
@@ -66,6 +59,15 @@ public:
     // ownership of the task.  Creating a new task cancels any previous ones.
     WebTaskRunner::Task* cancelAndCreate();
 
+protected:
+    // Only intended used by unit tests wanting to stack allocate and/or pass in a closure value.
+    // Please use the create() factory method elsewhere.
+    explicit CancellableTaskFactory(PassOwnPtr<Closure> closure)
+        : m_closure(closure)
+        , m_weakPtrFactory(this)
+    {
+    }
+
 private:
     class CancellableTask : public WebTaskRunner::Task {
         WTF_MAKE_NONCOPYABLE(CancellableTask);