Refactor ResourceLoadPriorityOptimizer to avoid walking render tree

Source/core/rendering/RenderImage.cpp

Index: Source/core/rendering/RenderImage.cpp
diff --git a/Source/core/rendering/RenderImage.cpp b/Source/core/rendering/RenderImage.cpp
index 5b6cff8a85de4e8dabbbf48b635f6289a1640a6d..96ee0a3994aa2b3e83cd8c0cc2a117a3e4620d6a 100644
--- a/Source/core/rendering/RenderImage.cpp
+++ b/Source/core/rendering/RenderImage.cpp
@@ -63,6 +63,7 @@ RenderImage::RenderImage(Element* element)
     , m_imageDevicePixelRatio(1.0f)
 {
     updateAltText();
+    resourceLoadPriorityOptimizer()->addRenderObject(this);
 }
 
 RenderImage* RenderImage::createAnonymous(Document* document)
@@ -74,6 +75,7 @@ RenderImage* RenderImage::createAnonymous(Document* document)
 
 RenderImage::~RenderImage()
 {
+    resourceLoadPriorityOptimizer()->removeRenderObject(this);

[esprehn, 2014/01/15 01:27:45]

This should be in ~RenderObject and you should just check that bitfield. That
way we can never forget a renderer.

[shatch, 2014/01/15 19:28:52]

Done.

     ASSERT(m_imageResource);
     m_imageResource->shutdown();
 }
@@ -578,22 +580,10 @@ void RenderImage::layout()
     updateInnerContentRect();
 }
 
-void RenderImage::didLayout(ResourceLoadPriorityOptimizer& optimizer)
-{
-    RenderReplaced::didLayout(optimizer);
-    updateImageLoadingPriority(optimizer);
-}
-
-void RenderImage::didScroll(ResourceLoadPriorityOptimizer& optimizer)
-{
-    RenderReplaced::didScroll(optimizer);
-    updateImageLoadingPriority(optimizer);
-}
-
-void RenderImage::updateImageLoadingPriority(ResourceLoadPriorityOptimizer& optimizer)
+bool RenderImage::updateImageLoadingPriorities()
 {
     if (!m_imageResource || !m_imageResource->cachedImage() || m_imageResource->cachedImage()->isLoaded())
-        return;
+        return false;
 
     LayoutRect viewBounds = viewRect();
     LayoutRect objectBounds = absoluteContentBox();
@@ -609,7 +599,9 @@ void RenderImage::updateImageLoadingPriority(ResourceLoadPriorityOptimizer& opti
     ResourceLoadPriorityOptimizer::VisibilityStatus status = isVisible ?
         ResourceLoadPriorityOptimizer::Visible : ResourceLoadPriorityOptimizer::NotVisible;
 
-    optimizer.notifyImageResourceVisibility(m_imageResource->cachedImage(), status);
+    resourceLoadPriorityOptimizer()->notifyImageResourceVisibility(m_imageResource->cachedImage(), status);
+
+    return true;
 }
 
 void RenderImage::computeIntrinsicRatioInformation(FloatSize& intrinsicSize, double& intrinsicRatio, bool& isPercentageIntrinsicSize) const