✨ feat: collect LCP subparts RUM-13818

[HugoGarrido]

Motivation

LCP Subparts are values that compute the final LCP measure the browser SDK.

This is helpful for troubleshooting LCP since it help to define what type of LCP issue we are facing (server, render etc.) by looking at the biggest contributor (more details in this doc)

Here is a breakdown of each part :

Subpart	Meaning
TTFB	Already tracked by the Browser SDK as firstByte
Resource load delay	Time between firstByte and the loading start of the resource associated with the LCP. 0 if no resource are attached to the LCP
Resource load duration	Time to takes to load the resource attached to the LCP0 if no resource are attached to the LCP
Element render delay	Time between the LCP resource finishes loading and the LCP element is fully rendered

This PR adds the collection of the LCP subparts when we collect the LCP

Changes

• In trackLargestContentfulPaint when we have an LCP entry :
  • re-measure the TTFB (keeping the name firstByte)
  • get the performance entry related to the LCP resource if applicable
  • compute an optional subParts object that is added in the final payload
• Extract a helper to safely compute the firstByte value
• Extract a helper to safely read performance global
• Update tests, fixtures and types to support the new subParts object

Test instructions

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	164.36 KiB	164.94 KiB	+591 B	+0.35%	✅
Rum Profiler	4.33 KiB	4.33 KiB	0 B	0.00%	✅
Rum Recorder	24.27 KiB	24.27 KiB	0 B	0.00%	✅
Logs	56.14 KiB	56.14 KiB	0 B	0.00%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	121.57 KiB	122.12 KiB	+562 B	+0.45%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0042	0.0044	+4.76%
RUM - add action	0.0135	0.0145	+7.41%
RUM - add error	0.0131	0.0139	+6.11%
RUM - add timing	0.0029	0.0036	+24.14%
RUM - start view	0.0043	0.0042	-2.33%
RUM - start/stop session replay recording	0.0008	0.0009	+12.50%
Logs - log message	0.0147	0.0217	+47.62%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	26.27 KiB	28.31 KiB	+2.04 KiB
RUM - add action	48.61 KiB	49.68 KiB	+1.06 KiB
RUM - add timing	24.97 KiB	25.15 KiB	+186 B
RUM - add error	54.76 KiB	54.43 KiB	-340 B
RUM - start/stop session replay recording	23.95 KiB	24.52 KiB	+583 B
RUM - start view	424.85 KiB	424.49 KiB	-370 B
Logs - log message	95.72 KiB	44.82 KiB	-50.90 KiB

🔗 RealWorld

[datadog-official]

⚠️ Tests

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 1 Test failed

remote configuration › should resolve an option value from js variable from rum/remoteConfiguration.scenario.ts (Datadog) (Fix with Cursor)

createTest.ts:244:3 should resolve an option value from js variable

[Webkit] › ../lib/framework/createTest.ts:244:3 › remote configuration › should resolve an option value from js variable 

    Error: expect(received).toBe(expected) // Object.is equality

    Expected: "js-version"
    Received: undefined

       at rum/remoteConfiguration.scenario.ts:93
...

ℹ️ Info

❄️ No new flaky tests detected

🎯 Code Coverage
• Patch Coverage: 72.73%
• Overall Coverage: 77.30% (+0.04%)

View detailed report

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[HugoGarrido]

I have read the CLA Document and I hereby sign the CLA