Make ResourceLoadPriority calculation simpler

third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp

Index: third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp b/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
index 554ef07d132cb9a38bbd276a051c2edb736dd222..589ea99e008648988db180e6bbd06ce8cdda23ec 100644
--- a/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
+++ b/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
@@ -135,14 +135,6 @@ static ResourceLoadPriority typeToPriority(Resource::Type type)
 
 ResourceLoadPriority ResourceFetcher::loadPriority(Resource::Type type, const FetchRequest& request, ResourcePriority::VisibilityStatus visibility)
 {
-    // TODO(yoav): Change it here so that priority can be changed even after it was resolved.
-    if (request.priority() != ResourceLoadPriorityUnresolved)
-        return request.priority();
-
-    // Synchronous requests should always be max priority, lest they hang the renderer.
-    if (request.options().synchronousPolicy == RequestSynchronously)
-        return ResourceLoadPriorityHighest;
-
     ResourceLoadPriority priority = typeToPriority(type);
 
     // Visible resources (images in practice) get a boost to High priority.
@@ -165,9 +157,11 @@ ResourceLoadPriority ResourceFetcher::loadPriority(Resource::Type type, const Fe
             priority = ResourceLoadPriorityLow;
         else if (request.forPreload() && m_imageFetched)
             priority = ResourceLoadPriorityMedium;
+    } else if (FetchRequest::LazyLoad == request.defer()) {
+        priority = ResourceLoadPriorityVeryLow;
     }
 
-    return context().modifyPriorityForExperiments(priority);
+    return std::max(context().modifyPriorityForExperiments(priority), request.resourceRequest().priority());

[kinuko, 2016/06/17 05:40:47]

Is the max here to cover synchronous load case?

[Nate Chapin, 2016/06/17 18:38:16]

That's half of it. Also, it covers the case where an image moves into the
viewport, then out of it, which would drop the priority this function reports.

[kinuko, 2016/06/20 04:28:31]

Ah I see, thanks. Would it make sense to add a brief comment about that? That
sounds helpful.

[Nate Chapin, 2016/06/20 19:44:31]

Done.

 }
 
 static void populateResourceTiming(ResourceTimingInfo* info, Resource* resource)
@@ -422,8 +416,7 @@ Resource* ResourceFetcher::requestResource(FetchRequest& request, const Resource
         return nullptr;
 
     unsigned long identifier = createUniqueIdentifier();
-    request.setPriority(loadPriority(factory.type(), request, ResourcePriority::NotVisible));
-    request.mutableResourceRequest().setPriority(request.priority());
+    request.mutableResourceRequest().setPriority(loadPriority(factory.type(), request, ResourcePriority::NotVisible));
     initializeResourceRequest(request.mutableResourceRequest(), factory.type(), request.defer());
     context().willStartLoadingResource(identifier, request.mutableResourceRequest(), factory.type());
     if (!request.url().isValid())
@@ -499,8 +492,8 @@ Resource* ResourceFetcher::requestResource(FetchRequest& request, const Resource
         // isn't at the same priority as the in-flight request, only allow promotions.
         // This can happen when a visible image's priority is increased and then another
         // reference to the image is parsed (which would be at a lower priority).
-        if (request.priority() > resource->resourceRequest().priority())
-            resource->didChangePriority(request.priority(), 0);
+        if (request.resourceRequest().priority() > resource->resourceRequest().priority())
+            resource->didChangePriority(request.resourceRequest().priority(), 0);
     }
 
     // If only the fragment identifiers differ, it is the same resource.