Bug 1722322 - Implement LargestContentfulPaint r=emilio

Spec: https://w3c.github.io/largest-contentful-paint

Differential Revision: https://phabricator.services.mozilla.com/D151079

layout/generic/nsImageFrame.cpp

@@ -27,6 +27,7 @@
 #include "mozilla/dom/HTMLImageElement.h"
 #include "mozilla/dom/ReferrerInfo.h"
 #include "mozilla/dom/ResponsiveImageSelector.h"
+#include "mozilla/dom/LargestContentfulPaint.h"
 #include "mozilla/image/WebRenderImageProvider.h"
 #include "mozilla/layers/RenderRootStateManager.h"
 #include "mozilla/layers/WebRenderLayerManager.h"
@@ -1115,6 +1116,8 @@ void nsImageFrame::Notify(imgIRequest* aRequest, int32_t aType,
   }
 
   if (aType == imgINotificationObserver::LOAD_COMPLETE) {
+    LargestContentfulPaint::MaybeProcessImageForElementTiming(
+        static_cast<imgRequestProxy*>(aRequest), GetContent()->AsElement());
     uint32_t imgStatus;
     aRequest->GetImageStatus(&imgStatus);
     nsresult status =
@@ -2365,6 +2368,13 @@ bool nsDisplayImage::CreateWebRenderCommands(
       mImage->GetImageProvider(aManager->LayerManager(), decodeSize, svgContext,
                                region, flags, getter_AddRefs(provider));
 
+  if (nsCOMPtr<imgIRequest> currentRequest = frame->GetCurrentRequest()) {
+    LCPHelpers::FinalizeLCPEntryForImage(
+        frame->GetContent()->AsElement(),
+        static_cast<imgRequestProxy*>(currentRequest.get()),
+        GetDestRect() - ToReferenceFrame());
+  }
+
   // While we got a container, it may not contain a fully decoded surface. If
   // that is the case, and we have an image we were previously displaying which
   // has a fully decoded surface, then we should prefer the previous image.