Adds a WebPageScheduler and a WebFrameScheduler

public/platform/WebFrameScheduler.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebFrameScheduler_h
+#define WebFrameScheduler_h
+
+#include "WebCommon.h"
+
+#include <string>
+
+namespace blink {
+
+class WebTaskRunner;
+
+class BLINK_PLATFORM_EXPORT WebFrameScheduler {
+public:
+    virtual ~WebFrameScheduler() {}
+
+    // The scheduler may throttle tasks associated with offscreen frames.
+    virtual void setFrameVisible(bool) {}
+
+    // Returns the WebTaskRunner for loading tasks.
+    // WebFrameScheduler owns the returned WebTaskRunner.
+    virtual WebTaskRunner* loadingTaskRunner() { return nullptr; }
+
+    // Returns the WebTaskRunner for timer tasks.
+    // WebFrameScheduler owns the returned WebTaskRunner.
+    virtual WebTaskRunner* timerTaskRunner() { return nullptr; }
+
+    // Record the current origin. This is for tracing.
+    virtual void setFrameOrigin(const std::string&) { }

[Mike West, 2015/09/07 07:45:18]

Nit: Be consistent, please. Either `{}` or `{ }` throughout (but I couldn't care
less which you choose. :) ).

`setFrameOrigin` worries me. Especially when it takes a string. What's the
expected use-case of this method? Does it need to care about things like
sandboxing? Would it be reasonable to take a `WebSecurityOrigin` instead of a
String?

[alex clarke (OOO till 29th), 2015/09/08 15:58:05]

Currently it's for annotating task queues in tracing.  I.e. you can see when a
task runs it was associated with foo.com.  This can be useful for diagnosing the
performance of a page with many iframes.

Yes this can take a WebSecurityOrigin.  Done. 

+};
+
+} // namespace blink
+
+#endif // WebFrameScheduler_h