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..32536b6d1095a7d3731c7a794c2beb6b4c54e015 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 unusedPreloadTimeoutInSeconds = 3;
+
 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 +1341,16 @@ void LocalDOMWindow::removedEventListener(const AtomicString& eventType, const R
     }
 }
 
+void LocalDOMWindow::warnUnusedPreloads(TimerBase* base)
+{
+    if (frame() && frame()->loader().documentLoader()) {
+        ResourceFetcher* fetcher = frame()->loader().documentLoader()->fetcher();
+        DCHECK(fetcher);
+        if (fetcher->hasUnusedLinkPreloads())
+            fetcher->warnUnusedPreloads();
+    }
+}
+
 void LocalDOMWindow::dispatchLoadEvent()
 {
     Event* loadEvent(Event::create(EventTypeNames::load));
@@ -1345,6 +1360,9 @@ void LocalDOMWindow::dispatchLoadEvent()
         timing.markLoadEventStart();
         dispatchEvent(loadEvent, document());
         timing.markLoadEventEnd();
+        DCHECK(documentLoader->fetcher());

[Nate Chapin, 2016/09/14 22:14:31]

I'd skip scheduling the timer here if documentLoader !=
frame()->loader().documentLoader() after dispatchEvent().

Also, should the Timer be cancelled somewhere in the case where a new navigation
commits before it fires?

[Yoav Weiss, 2016/09/15 06:11:29]

added such a check
Normally a detach would call clearPreloads which would result in the counter
being 0.
So in such a case the timer would fire but do nothing. Nevertheless, now
stopping the timer on clearDocument().

+        if (documentLoader->fetcher()->hasUnusedLinkPreloads())
+            m_unusedPreloadsTimer.startOneShot(unusedPreloadTimeoutInSeconds, BLINK_FROM_HERE);
     } else {
         dispatchEvent(loadEvent, document());
     }