Fix Resource Priorities and Scheduling (Blink Side)

Source/core/fetch/ResourceLoadPriorityOptimizer.cpp

Index: Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
diff --git a/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp b/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
index 721386ed1f684e72d47d52ed423ce3482c1c7656..3a1dc11cf67e0d36da490009e291e76035b6bf89 100644
--- a/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
+++ b/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
@@ -30,6 +30,7 @@
 
 #include "config.h"
 #include "core/fetch/ResourceLoadPriorityOptimizer.h"
+#include "core/frame/Settings.h"
 #include "core/layout/LayoutObject.h"
 #include "platform/TraceEvent.h"
 
@@ -55,6 +56,8 @@ ResourceLoadPriorityOptimizer::ResourceAndVisibility::~ResourceAndVisibility()
 }
 
 ResourceLoadPriorityOptimizer::ResourceLoadPriorityOptimizer()
+    : m_retrievedSettings(false)
+    , m_increaseFetchPriorities(false)
 {
 }
 
@@ -64,6 +67,10 @@ ResourceLoadPriorityOptimizer::~ResourceLoadPriorityOptimizer()
 
 void ResourceLoadPriorityOptimizer::addLayoutObject(LayoutObject* layoutObject)
 {
+    if (!m_retrievedSettings) {
+        m_increaseFetchPriorities = layoutObject->document().settings()->fetchIncreasePriorities();
+        m_retrievedSettings = true;
+    }
     m_objects.add(layoutObject);
     layoutObject->setHasPendingResourceUpdate(true);
 }
@@ -98,6 +105,12 @@ void ResourceLoadPriorityOptimizer::updateImageResourcesWithLoadPriority()
         ResourceLoadPriority priority = resource.value->status == Visible ?
             ResourceLoadPriorityLow : ResourceLoadPriorityVeryLow;
 
+        ASSERT(m_retrievedSettings);

[Bryan McQuade, 2015/08/11 13:05:12]

I think this assert is important given that we depend on the value having been
read and set here, but are we sure this will never fire? can
updateImageResourcesWithLoadPriority ever get called without a prior call to
addLayoutObject?

[Pat Meenan, 2015/08/11 14:18:40]

I'm not sure the ASSERT is even needed.  updateImageResourcesWithLoadPriority is
private and is only called from the updateAllImageResourcePriorities function
above.  updateAllImageResourcePriorities starts with an empty list of image
resources and walks the layout objects to build the list of imageResources. 
It's impossible for there to be any elements in m_imageResources without
addLayoutObject having been called.

I actually removed the assert because of that but I'd be willing to put it back
in if you think it's necessary to protect against though someone would have to
radically change the logic for it to be needed.

+        if (m_increaseFetchPriorities) {
+            priority = resource.value->status == Visible ?
+                ResourceLoadPriorityHigh : ResourceLoadPriorityLow;
+        }
+
         if (priority != resource.value->imageResource->resourceRequest().priority()) {
             resource.value->imageResource->mutableResourceRequest().setPriority(priority, resource.value->screenArea);
             resource.value->imageResource->didChangePriority(priority, resource.value->screenArea);