Refactor the API for setting dynamic resource load priorities

Source/core/fetch/Resource.cpp

Index: Source/core/fetch/Resource.cpp
diff --git a/Source/core/fetch/Resource.cpp b/Source/core/fetch/Resource.cpp
index 7d8efd2fd1dfa91faf023202a6058f445deac03c..5224595219fc6f5262e05d2beaee958390e0d10d 100644
--- a/Source/core/fetch/Resource.cpp
+++ b/Source/core/fetch/Resource.cpp
@@ -954,6 +954,20 @@ void Resource::didChangePriority(ResourceLoadPriority loadPriority, int intraPri
         m_loader->didChangePriority(loadPriority, intraPriorityValue);
 }
 
+ResourcePriority Resource::priorityFromClients()
+{
+    ResourcePriority priority;
+    ResourceClientWalker<ResourceClient> w(m_clients);
+    while (ResourceClient* c = w.next()) {
+        ResourcePriority nextPriority = c->updatePriority(this);
+        if (nextPriority.visibility == ResourcePriority::NotVisible)
+            continue;
+        priority.visibility = ResourcePriority::Visible;
+        priority.intraPriorityValue += nextPriority.intraPriorityValue;
+    }
+    return priority;
+}
+
 Resource::ResourceCallback* Resource::ResourceCallback::callbackHandler()
 {
     DEFINE_STATIC_LOCAL(OwnPtrWillBePersistent<ResourceCallback>, callbackHandler, (adoptPtrWillBeNoop(new ResourceCallback)));