Raise the loading priority of in-viewport images.

Source/core/fetch/ResourceLoadPriorityOptimizer.h

Index: Source/core/fetch/ResourceLoadPriorityOptimizer.h
diff --git a/Source/core/rendering/SubtreeLayoutScope.h b/Source/core/fetch/ResourceLoadPriorityOptimizer.h
similarity index 66%
copy from Source/core/rendering/SubtreeLayoutScope.h
copy to Source/core/fetch/ResourceLoadPriorityOptimizer.h
index c073b7f4cf1e801517c5e8654504b7f3b3ae7ed7..e5b99314934894d8a0fb9f60a6a83360410af42c 100644
--- a/Source/core/rendering/SubtreeLayoutScope.h
+++ b/Source/core/fetch/ResourceLoadPriorityOptimizer.h
@@ -28,41 +28,39 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef SubtreeLayoutScope_h
-#define SubtreeLayoutScope_h
+#ifndef ResourceLoadPriorityOptimizer_h
+#define ResourceLoadPriorityOptimizer_h
 
-#include "wtf/HashSet.h"
+#include "core/fetch/ImageResource.h"
+#include "core/fetch/ResourcePtr.h"
 
-// This is the way to mark a subtree as needing layout during layout,
-// e.g. for the purposes of doing a multipass layout.
-//
-// It should only be used during layout. Outside of layout, you should
-// just call renderer->setNeedsLayout() directly.
-//
-// It ensures that you don't accidentally mark part of the tree as
-// needing layout and not actually lay it out.
+#include "wtf/HashMap.h"
 
 namespace WebCore {
 
-class RenderObject;
-
-class SubtreeLayoutScope {
+class ResourceLoadPriorityOptimizer {
 public:
-    SubtreeLayoutScope(RenderObject* root);
-    ~SubtreeLayoutScope();
-
-    void setNeedsLayout(RenderObject* descendant);
-    void setChildNeedsLayout(RenderObject* descendant);
-
-    RenderObject* root() { return m_root; }
-    void addRendererToLayout(RenderObject* renderer);
+    enum VisibilityStatus {
+        NotVisible,
+        Visible,
+    };
+    ResourceLoadPriorityOptimizer();
+    ~ResourceLoadPriorityOptimizer();
+    void notifyImageResourceVisibility(ImageResource*, VisibilityStatus);
 
 private:
-    RenderObject* m_root;
+    void updateImageResourcesWithLoadPriority();
 
-#ifndef NDEBUG
-    HashSet<RenderObject*> m_renderersToLayout;
-#endif
+    struct ResourceAndVisibility {
+        ResourceAndVisibility(ImageResource*, VisibilityStatus);
+        ResourceAndVisibility();
+        ~ResourceAndVisibility();
+        ResourcePtr<ImageResource> imageResource;
+        VisibilityStatus status;
+    };
+
+    typedef WTF::HashMap<unsigned long, ResourceAndVisibility> ImageResourceMap;

[abarth-chromium, 2013/12/02 19:34:56]

Rather than using ResourceAndVisibility, you should store an
OwnPtr<ResourceAndVisibility>.  That has a couple benefits:

1) You don't need to write hash traits for ResourceAndVisibility because OwnPtr
already has them.
2) The table will use less memory.  HashMap stores the values inline, which
means the empty slots in the table are bloated by the size of the value.

Also, WTF::HashMap -> HashMap

[shatch, 2013/12/02 22:32:46]

Cool, thanks for the explanation! Done.

+    ImageResourceMap m_imageResources;
 };
 
 }