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

Source/core/rendering/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
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  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 278 matching lines @@
     return false;
 }
 
 bool RenderLayerCompositor::canRender3DTransforms() const
 {
     return hasAcceleratedCompositing() && (m_compositingTriggers & ChromeClient::ThreeDTransformTrigger);
 }
 
 void RenderLayerCompositor::setCompositingLayersNeedRebuild(bool needRebuild)
 {
+    // FIXME: this code needs to be carefully merged with setNeedsCompositingUpdate.

[jamesr, 2014/02/11 01:50:14]

I don't really understand what this comment is trying to convey.  Is there a bug
on this issue? Could you just have a reference to that bug here?

     if (inCompositingMode())
         m_compositingLayersNeedRebuild = needRebuild;
+
+    m_renderView->frameView()->scheduleAnimation();
 }
 
 void RenderLayerCompositor::updateCompositingRequirementsState()
 {
     if (!m_needsUpdateCompositingRequirementsState)
         return;
 
     TRACE_EVENT0("blink_rendering,comp-scroll", "RenderLayerCompositor::updateCompositingRequirementsState");
 
     m_needsUpdateCompositingRequirementsState = false;
@@ skipping 67 matching lines @@
         break;
     case CompositingUpdateOnScroll:
         m_needsToRecomputeCompositingRequirements = true; // Overlap can change with scrolling, so need to check for hierarchy updates.
         m_needsToUpdateLayerTreeGeometry = true;
         break;
     case CompositingUpdateOnCompositedScroll:
         m_needsToUpdateLayerTreeGeometry = true;
         break;
     }
 
-    // FIXME: some senior devs are suggesting that we need to always schedule a frame here.
-    // but we do seem to reach this point in code when frames are unnecessary and
-    // we need to resolve those instances before initiating a frame here, otherwise
-    // performance will regress by forcing unnecessary frames.
+    m_renderView->frameView()->scheduleAnimation();
 }
 
 void RenderLayerCompositor::updateCompositingLayers()
 {
     TRACE_EVENT0("blink_rendering", "RenderLayerCompositor::updateCompositingLayers");
 
     // FIXME: We should carefully clean up the awkward early-exit semantics, balancing
     // between skipping unnecessary compositing updates and not incorrectly skipping
     // necessary updates.
 
@@ skipping 2293 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "Frame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore