If a compositing update is declared as needed, scheduleAnimation should be triggered.

public/web/WebWidgetClient.h

Index: public/web/WebWidgetClient.h
diff --git a/public/web/WebWidgetClient.h b/public/web/WebWidgetClient.h
index 0e455838e12612206d0389ceafc15d7979bc3492..cbc98b8a3f33bb8a74a4e7f7810b5d0e044046fd 100644
--- a/public/web/WebWidgetClient.h
+++ b/public/web/WebWidgetClient.h
@@ -101,6 +101,11 @@ public:
     // Called when a call to WebWidget::animate is required
     virtual void scheduleAnimation() { }
 
+    // Called to query the state of the rendering back-end. Should return true
+    // when scheduleAnimation (or possibly some other cause for another frame)
+    // was called, but before WebWidget::animate actually does a frame.
+    virtual bool isCompositorFramePending() const { return false; }
+
     // Called when the widget acquires or loses focus, respectively.
     virtual void didFocus() { }
     virtual void didBlur() { }