Changing animate to beginFrame and use struct rather than naked double to allow extension.

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)
+        : lastFrameTimeMonotonic(lastFrameTimeMonotonic)
+    { }
+
+    // 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;
+};
+
+} // namespace blink
+
+#endif