Use the scheduling mechanism provided by the platform

public/platform/Platform.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 74 matching lines @@
 class WebMediaStreamCenterClient;
 class WebMessagePortChannel;
 class WebMimeRegistry;
 class WebNotificationPresenter;
 class WebPluginListBuilder;
 class WebPrescientNetworking;
 class WebPublicSuffixList;
 class WebRTCPeerConnectionHandler;
 class WebRTCPeerConnectionHandlerClient;
 class WebSandboxSupport;
+class WebScheduler;
 class WebSecurityOrigin;
 class WebScrollbarBehavior;
 class WebSocketHandle;
 class WebSocketStreamHandle;
 class WebSpeechSynthesizer;
 class WebSpeechSynthesizerClient;
 class WebStorageNamespace;
 struct WebFloatPoint;
 class WebThemeEngine;
 class WebThread;
@@ skipping 248 matching lines @@
     // Creates an embedder-defined thread.
     virtual WebThread* createThread(const char* name) { return 0; }
 
     // Returns an interface to the current thread. This is owned by the
     // embedder.
     virtual WebThread* currentThread() { return 0; }
 
     // Yield the current thread so another thread can be scheduled.
     virtual void yieldCurrentThread() { }
 
+    // May return null.

[eseidel, 2014/10/21 16:11:02]

I think instead of letting this return null and needing to check null everywhere
we should consider just having a dummy scheduler like we do for EmptyClients.

[Sami, 2014/10/21 18:49:34]

That's a great idea. Since it doesn't look like we can easily return anything
non-null from here, I've chosen to keep a helper in
platform/scheduler/Scheduler.h which will transparently fall back if the
platform doesn't provide a real scheduler (which is the case when we first land
this patch).

The helper also makes sense because we can translate between Blink and Web types
there.

+    virtual WebScheduler* scheduler() { return 0; }
 
     // WaitableEvent -------------------------------------------------------
 
     // Creates an embedder-defined waitable event object.
     virtual WebWaitableEvent* createWaitableEvent() { return 0; }
 
     // Waits on multiple events and returns the event object that has been
     // signaled. This may return 0 if it fails to wait events.
     // Any event objects given to this method must not deleted while this
     // wait is happening.
@@ skipping 266 matching lines @@
 
     virtual WebGeofencingProvider* geofencingProvider() { return 0; }
 
 protected:
     virtual ~Platform() { }
 };
 
 } // namespace blink
 
 #endif