Make ResourceLoadPriority calculation simpler

third_party/WebKit/Source/core/loader/LinkLoader.cpp

Index: third_party/WebKit/Source/core/loader/LinkLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/LinkLoader.cpp b/third_party/WebKit/Source/core/loader/LinkLoader.cpp
index fb6549e54502baa420190857417aa49970623f6a..f563594fe16ac0f7c60b651ff49c5beb7ca29792 100644
--- a/third_party/WebKit/Source/core/loader/LinkLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/LinkLoader.cpp
@@ -297,7 +297,8 @@ static Resource* preloadIfNeeded(const LinkRelAttribute& relAttribute, const KUR
         document.addConsoleMessage(ConsoleMessage::create(OtherMessageSource, DebugMessageLevel, String("Preload triggered for " + href.host() + href.path())));
     linkRequest.setForPreload(true, monotonicallyIncreasingTime());
     linkRequest.setLinkPreload(true);
-    linkRequest.setPriority(document.fetcher()->loadPriority(resourceType, linkRequest));
+    if (resourceType == Resource::LinkPreload)
+        linkRequest.setDefer(FetchRequest::LazyLoad);

[Yoav Weiss, 2016/06/25 08:37:59]

Why should we mark LinkPreload resources as LazyLoad? They should be a
functional equivalent of XHRs.

[Pat Meenan, 2016/06/27 14:56:55]

+1.  I think you may have been thinking about prefetch (which is a hint and low
priority) vs preload (which is a declarative fetch).  It may also be confusing
because we use "forPreload" internally as being an indicator that it was from
the preload scanner (and not a link rel=preload).

[Nate Chapin, 2016/06/27 19:46:16]

Ok, so the comment in LinkLoaderTest says rel=preload should be priority
VeryLow, the test actually asserts that it should be Low, and this comment
thread it should be functionally equivalent to XHRs, which are priority High.
Which would you like? :)

Updated the LazyLoad logic in computeLoadPriority() to make Raw LazyLoads Low
instead of VeryLow, to keep the current behavior. Feel free to override that
default action :)

     return document.loader()->startPreload(resourceType, linkRequest);
 }