[blink] Request compositing update when canvas hibernates/wakes up.

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 1198 matching lines @@
     return;
 
   bool hidden = !page()->isPageVisible();
   m_context->setIsHidden(hidden);
   if (hidden) {
     clearCopiedImage();
     if (is3D()) {
       discardImageBuffer();
     }
   }
+  // If visibility changes, shouldBeDirectComposited() may change.
+  setNeedsCompositingUpdate();

[chrishtr, 2017/04/07 17:12:32]

Which of the conditions below depend on page visibility?

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/html/HTML...

[Eric Seckler, 2017/04/07 17:27:11]

CanvasRenderingContext2D::isComposited() -> isAccelerated() ->
ImageBuffer::isAccelerated() -> Canvas2DImageBufferSurface::isAccelerated() ->
Canvas2DLayerBridge::isAccelerated() -> isHibernating()

And Canvas2DLayerBridge::hibernate() is eventually called by setIsHidden()
above.

 }
 
 void HTMLCanvasElement::contextDestroyed(ExecutionContext*) {
   if (m_context)
     m_context->stop();
 }
 
 void HTMLCanvasElement::styleDidChange(const ComputedStyle* oldStyle,
                                        const ComputedStyle& newStyle) {
   if (m_context)
@@ skipping 244 matching lines @@
     // Creates a placeholder layer first before Surface is created.
     m_surfaceLayerBridge->createSolidColorLayer();
   }
 }
 
 void HTMLCanvasElement::OnWebLayerReplaced() {
   setNeedsCompositingUpdate();
 }
 
 }  // namespace blink