Adds a CancellableTaskFactory and exposes postLoadingTasks to Blink

Source/platform/scheduler/Scheduler.cpp

Index: Source/platform/scheduler/Scheduler.cpp
diff --git a/Source/platform/scheduler/Scheduler.cpp b/Source/platform/scheduler/Scheduler.cpp
index 535f114114da747340502f20efd830cbf81440d0..98da04f82f8437f02e52a02d9c93af1833736767 100644
--- a/Source/platform/scheduler/Scheduler.cpp
+++ b/Source/platform/scheduler/Scheduler.cpp
@@ -32,6 +32,25 @@ private:
     OwnPtr<Scheduler::IdleTask> m_task;
 };
 
+class ClosureRunner : public WebThread::Task {

[rmcilroy, 2015/01/26 18:09:01]

nit - ClosureRunnerTask (if you take my suggestion to expose this class as a top
level class).

[alex clarke (OOO till 29th), 2015/01/27 11:41:19]

Done.

+public:

[jochen (gone - plz use gerrit), 2015/01/26 15:53:31]

non-copyable

[alex clarke (OOO till 29th), 2015/01/26 17:00:45]

Done.

+    explicit ClosureRunner(PassOwnPtr<Closure> closure) : m_closure(closure)
+    {
+    }
+
+    virtual ~ClosureRunner()
+    {
+    }
+
+    // WebThread::Task implementation.
+    void run() override
+    {
+        (*m_closure)();
+    }
+private:
+    OwnPtr<Closure> m_closure;
+};
+
 Scheduler* Scheduler::s_sharedScheduler = nullptr;
 
 void Scheduler::shutdown()
@@ -64,6 +83,12 @@ void Scheduler::postIdleTask(const TraceLocation& location, PassOwnPtr<IdleTask>
         m_webScheduler->postIdleTask(WebTraceLocation(location), new IdleTaskRunner(idleTask));
 }
 
+void Scheduler::postLoadingTask(const TraceLocation& location, PassOwnPtr<Closure> closure)
+{
+    if (m_webScheduler)
+        m_webScheduler->postLoadingTask(WebTraceLocation(location), new ClosureRunner(closure));
+}
+
 bool Scheduler::shouldYieldForHighPriorityWork() const
 {
     if (m_webScheduler)