[devtools] Fix LCP in Performance Timing

This patch adds the navigationId to LCP events to allow
reporting of LCP for every navigation.

Bug: chromium:1001010
Change-Id: If813f679d75c45bbb16a270576f5c9be0f47c772
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1790445
Commit-Queue: Jan Scheffler <janscheffler@google.com>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Liquan (Max) Gu <maxlg@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697507}

third_party/blink/renderer/core/paint/largest_contentful_paint_calculator.cc

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 #include "third_party/blink/renderer/core/paint/largest_contentful_paint_calculator.h"
-
+#include "third_party/blink/renderer/core/inspector/identifiers_factory.h"
 #include "third_party/blink/renderer/core/paint/image_element_timing.h"
 
 namespace blink {
@@ -189,6 +189,9 @@ LargestContentfulPaintCalculator::TextCandidateTraceData() {
   value->SetInteger("candidateIndex", ++count_candidates_);
   value->SetBoolean("isMainFrame",
                     window_performance_->GetFrame()->IsMainFrame());
+  auto* document = window_performance_->DomWindow()->document();
+  value->SetString("navigationId",
+                   IdentifiersFactory::LoaderId(document->Loader()));
   return value;
 }
 
@@ -201,6 +204,10 @@ LargestContentfulPaintCalculator::ImageCandidateTraceData() {
   value->SetInteger("candidateIndex", ++count_candidates_);
   value->SetBoolean("isMainFrame",
                     window_performance_->GetFrame()->IsMainFrame());
+  auto* document = window_performance_->DomWindow()->document();
+  value->SetString("navigationId",
+                   IdentifiersFactory::LoaderId(document->Loader()));
+
   return value;
 }
 
@@ -210,6 +217,10 @@ LargestContentfulPaintCalculator::InvalidationTraceData() {
   value->SetInteger("candidateIndex", ++count_candidates_);
   value->SetBoolean("isMainFrame",
                     window_performance_->GetFrame()->IsMainFrame());
+  auto* document = window_performance_->DomWindow()->document();
+  value->SetString("navigationId",
+                   IdentifiersFactory::LoaderId(document->Loader()));
+
   return value;
 }
 

third_party/blink/renderer/devtools/front_end/timeline/TimelineFlameChartDataProvider.js

@@ -548,11 +548,20 @@ Timeline.TimelineFlameChartDataProvider = class extends Common.Object {
     // Only the LCP event with the largest candidate index is relevant.
     // Do not record an LCP event if it is an invalidate event.
     if (lcpEvents.length > 0) {
-      const winning_event = lcpEvents.reduce(function(a, b) {
-        return Number(a.args['data']['candidateIndex']) > Number(b.args['data']['candidateIndex']) ? a : b;
-      });
-      if (timelineModel.isLCPCandidateEvent(winning_event))
-        metricEvents.push(winning_event);
+      /** @type {!Map<string, !SDK.TracingModel.Event>} */
+      const lcpEventsByNavigationId = new Map();
+      for (const e of lcpEvents) {
+        const key = e.args['data']['navigationId'];
+        const previousLastEvent = lcpEventsByNavigationId.get(key);
+
+        if (!previousLastEvent || previousLastEvent.args['data']['candidateIndex'] < e.args['data']['candidateIndex'])
+          lcpEventsByNavigationId.set(key, e);
+      }
+
+      const latestCandidates = Array.from(lcpEventsByNavigationId.values());
+      const latestEvents = latestCandidates.filter(e => timelineModel.isLCPCandidateEvent(e));
+
+      metricEvents.push(...latestEvents);
     }
 
     metricEvents.sort(SDK.TracingModel.Event.compareStartTime);