Add a warning whenever link preloads are not used

third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp

Index: third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
diff --git a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
index 76827a89668652c30a26a5156694a0096f837c0d..cd12d6e62446833b7ee084ed542f12e4c1746991 100644
--- a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
+++ b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
@@ -47,6 +47,7 @@
 #include "core/events/PageTransitionEvent.h"
 #include "core/events/PopStateEvent.h"
 #include "core/events/ScopedEventQueue.h"
+#include "core/fetch/ResourceFetcher.h"
 #include "core/frame/BarProp.h"
 #include "core/frame/DOMVisualViewport.h"
 #include "core/frame/EventHandlerRegistry.h"
@@ -83,6 +84,9 @@
 
 namespace blink {
 
+// Timeout for link preloads to be used after window.onload
+static const int unusedPreloadTimeout = 3;

[Charlie Harrison, 2016/09/14 12:34:58]

Make it clear this is in seconds in the name or comment.

[Yoav Weiss, 2016/09/14 13:28:31]

good call

+
 class PostMessageTimer final : public GarbageCollectedFinalized<PostMessageTimer>, public SuspendableTimer {
     USING_GARBAGE_COLLECTED_MIXIN(PostMessageTimer);
 public:
@@ -260,6 +264,7 @@ bool LocalDOMWindow::allowPopUp()
 LocalDOMWindow::LocalDOMWindow(LocalFrame& frame)
     : m_frame(&frame)
     , m_visualViewport(DOMVisualViewport::create(this))
+    , m_unusedPreloadsTimer(this, &LocalDOMWindow::warnUnusedPreloads)
     , m_shouldPrintWhenFinishedLoading(false)
 {
     ThreadState::current()->registerPreFinalizer(this);
@@ -1336,6 +1341,14 @@ void LocalDOMWindow::removedEventListener(const AtomicString& eventType, const R
     }
 }
 
+void LocalDOMWindow::warnUnusedPreloads(TimerBase* base)
+{
+    if (frame() && frame()->loader().documentLoader()) {
+        DCHECK(frame()->loader().documentLoader()->fetcher());
+        frame()->loader().documentLoader()->fetcher()->warnUnusedPreloads();
+    }
+}
+
 void LocalDOMWindow::dispatchLoadEvent()
 {
     Event* loadEvent(Event::create(EventTypeNames::load));
@@ -1345,6 +1358,8 @@ void LocalDOMWindow::dispatchLoadEvent()
         timing.markLoadEventStart();
         dispatchEvent(loadEvent, document());
         timing.markLoadEventEnd();
+        m_unusedPreloadsTimer.startOneShot(unusedPreloadTimeout, BLINK_FROM_HERE);

[Charlie Harrison, 2016/09/14 12:34:58]

I think it makes sense to only dispatch this timer if there are link preloads
currently unmatched. The other cases seem extremely rare (like inserting it into
the dom after onload).

[Yoav Weiss, 2016/09/14 13:28:31]

It makes sense, but I really don't want to iterate over m_preloads twice...
I can add a linkPreloads counter that will be used here and at
warnUnusedPreloads() itself

[Charlie Harrison, 2016/09/14 13:32:59]

That's a good point. A counter is not great but I think it's better than issuing
no-op tasks for most page loads.

+
     } else {

[Charlie Harrison, 2016/09/14 12:34:58]

Remove empty line.

[Yoav Weiss, 2016/09/14 13:28:31]

sure

         dispatchEvent(loadEvent, document());
     }