Raise the loading priority of in-viewport images.

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 3f1f4682c575820ada4935ec99bb2e53c13a2022..2c27d384f1f40a2d531ab659b07cb2943585a24e 100644
--- a/Source/core/rendering/RenderImage.cpp
+++ b/Source/core/rendering/RenderImage.cpp
@@ -31,6 +31,8 @@
 #include "HTMLNames.h"
 #include "core/editing/FrameSelection.h"
 #include "core/fetch/ImageResource.h"
+#include "core/fetch/ResourceLoadPriorityOptimizer.h"
+#include "core/fetch/ResourceLoader.h"
 #include "core/html/HTMLAreaElement.h"
 #include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLInputElement.h"
@@ -573,6 +575,40 @@ 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)
+{
+    if (!m_imageResource || !m_imageResource->cachedImage() || m_imageResource->cachedImage()->isLoaded())
+        return;
+
+    LayoutRect viewBounds = viewRect();
+    LayoutRect objectBounds = absoluteContentBox();
+
+    // The object bounds might be empty right now, so intersects will fail since it doesn't deal
+    // with empty rects. Use LayoutRect::contains in that case.
+    bool isVisible;

[eseidel, 2013/12/10 17:15:30]

Same problem.  I wouldn't bother making empty rects visible.  They can't have
any affect on rendering, no?

[shatch, 2013/12/10 18:56:19]

Per offline discussion: I don't have any data on this either way at the moment,
but I was sort of leaning towards the idea that the rect is empty, but the
position is still somewhat valid, so in that case we'd want to bump up the
priority. Either way, we should investigate more in the near future to figure
out what's best.

+    if (!objectBounds.isEmpty())
+        isVisible =  viewBounds.intersects(objectBounds);
+    else
+        isVisible = viewBounds.contains(objectBounds);
+
+    ResourceLoadPriorityOptimizer::VisibilityStatus status = isVisible ?
+        ResourceLoadPriorityOptimizer::Visible : ResourceLoadPriorityOptimizer::NotVisible;
+
+    optimizer.notifyImageResourceVisibility(m_imageResource->cachedImage(), status);
+}
+
 void RenderImage::computeIntrinsicRatioInformation(FloatSize& intrinsicSize, double& intrinsicRatio, bool& isPercentageIntrinsicSize) const
 {
     RenderReplaced::computeIntrinsicRatioInformation(intrinsicSize, intrinsicRatio, isPercentageIntrinsicSize);