Add support for Low Priorirty tasks.

public/web/WebBeginFrameArgs.h

-// Copyright 2014 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 WebBeginFrameArgs_h
-#define WebBeginFrameArgs_h
-
-namespace blink {
-
-struct WebBeginFrameArgs {
-    WebBeginFrameArgs(double lastFrameTimeMonotonic, double deadline, double interval)
-        : lastFrameTimeMonotonic(lastFrameTimeMonotonic)
-        , deadline(deadline)
-        , interval(interval)
-    { }
-
-    // TODO: Remove this constructor once Chromium has been updated.
-    WebBeginFrameArgs(double lastFrameTimeMonotonic)
-        : lastFrameTimeMonotonic(lastFrameTimeMonotonic)
-        , deadline(0)
-        , interval(0)
-    { }
-
-    // FIXME: Upgrade the time in CLOCK_MONOTONIC values to use a TimeTick like
-    // class rather than a bare double.
-
-    // FIXME: Extend this class to include the fields from Chrome
-    // BeginFrameArgs structure.
-
-    // Time in CLOCK_MONOTONIC that is the most recent vsync time.
-    double lastFrameTimeMonotonic;
-
-    // Time in CLOCK_MONOTONIC by which the renderer should finish producing the current frame. 0 means a deadline wasn't set.
-    double deadline;
-
-    // Expected delta between two successive frame times. 0 if a regular interval isn't available.
-    double interval;
-};
-
-} // namespace blink
-
-#endif