Refactor the API for setting dynamic resource load priorities

Source/core/loader/FrameFetchContext.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 656 matching lines @@
 void FrameFetchContext::countClientHintsResourceWidth()
 {
     UseCounter::count(frame(), UseCounter::ClientHintsResourceWidth);
 }
 
 void FrameFetchContext::countClientHintsViewportWidth()
 {
     UseCounter::count(frame(), UseCounter::ClientHintsViewportWidth);
 }
 
-bool FrameFetchContext::fetchIncreasePriorities() const
-{
-    return frame()->settings() && frame()->settings()->fetchIncreasePriorities();
-}
-
-ResourceLoadPriority FrameFetchContext::modifyPriorityForExperiments(ResourceLoadPriority priority, Resource::Type type, const FetchRequest& request)
+ResourceLoadPriority FrameFetchContext::modifyPriorityForExperiments(ResourceLoadPriority priority, Resource::Type type, const FetchRequest& request, ResourcePriority::VisibilityStatus visibility)
 {
     // An image fetch is used to distinguish between "early" and "late" scripts in a document
     if (type == Resource::Image)
         m_imageFetched = true;
 
     // If Settings is null, we can't verify any experiments are in force.
     if (!frame()->settings())
         return priority;
 
     // If enabled, drop the priority of all resources in a subframe.
     if (frame()->settings()->lowPriorityIframes() && !frame()->isMainFrame())
         return ResourceLoadPriorityVeryLow;
 
     // Async/Defer scripts.
     if (type == Resource::Script && FetchRequest::LazyLoad == request.defer())
         return frame()->settings()->fetchIncreaseAsyncScriptPriority() ? ResourceLoadPriorityMedium : ResourceLoadPriorityLow;
 
     // Runtime experiment that change how we prioritize resources.
     // The toggles do not depend on each other and can be flipped individually
     // though the cumulative result will depend on the interaction between them.
     // Background doc: https://docs.google.com/document/d/1bCDuq9H1ih9iNjgzyAL0gpwNFiEP4TZS-YLRp_RuMlc/edit?usp=sharing
 
     // Increases the priorities for CSS, Scripts, Fonts and Images all by one level
     // and parser-blocking scripts and visible images by 2.
     // This is used in conjunction with logic on the Chrome side to raise the threshold
     // of "layout-blocking" resources and provide a boost to resources that are needed
     // as soon as possible for something currently on the screen.
     int modifiedPriority = static_cast<int>(priority);
-    if (fetchIncreasePriorities()) {
+    if (frame()->settings()->fetchIncreasePriorities()) {
         if (type == Resource::CSSStyleSheet || type == Resource::Script || type == Resource::Font || type == Resource::Image)
             modifiedPriority++;
     }
 
+    // Always give visible resources a bump, and an additional bump if generally increasing priorities.
+    if (visibility == ResourcePriority::Visible) {
+        modifiedPriority++;
+        if (frame()->settings()->fetchIncreasePriorities())
+            modifiedPriority++;
+    }
+
     if (frame()->settings()->fetchIncreaseFontPriority() && type == Resource::Font)
         modifiedPriority++;
 
     if (type == Resource::Script) {
         // Reduce the priority of late-body scripts.
         if (frame()->settings()->fetchDeferLateScripts() && request.forPreload() && m_imageFetched)
             modifiedPriority--;
         // Parser-blocking scripts.
-        if (fetchIncreasePriorities() && !request.forPreload())
+        if (frame()->settings()->fetchIncreasePriorities() && !request.forPreload())
             modifiedPriority++;
     }
 
     // Clamp priority
     modifiedPriority = std::min(static_cast<int>(ResourceLoadPriorityHighest), std::max(static_cast<int>(ResourceLoadPriorityLowest), modifiedPriority));
     return static_cast<ResourceLoadPriority>(modifiedPriority);
 }
 
 DEFINE_TRACE(FrameFetchContext)
 {
     visitor->trace(m_document);
     visitor->trace(m_documentLoader);
     FetchContext::trace(visitor);
 }
 
 } // namespace blink