[perf, epic] Investigate the startup performance

[atuchin-m]

The perf tests (system_health.common_health) shows that we use much more CPU during the startup.
Mac x64, cr117: Chrome 909.155ms, Brave: 2,160ms, Brave-no-adblock: 1,368ms
That could have a visible impact on user experience (especially on Android, when app restart is a usual thing)

The goals are:

• find the main contributors into the difference;
• create issues, discuss and optimize or help to optimize;
• setup more precise instruments to track startup performance and to prevent future degradation .

This is meta issue to link all the related work.

[atuchin-m]

Some related work:

1. CPU usage perf test (startup is included): Perf: enable system_health.common_desktop to perf CI and update WPRs  #30969
2. loading.desktop.brave.startup perf test to see page loading timing just after the startup: Add a perf test to measure startup page loading timings #33651

[atuchin-m]

system_health.common_health shows that 95% of CPU is taken by the browser process (both Brave & Chrome).
So the browser process looks like a primary target to focus on.

One important thing to check: do we correctly count CPU usage of short-living processes (like DataDecoder) that are ended to the moment we end the perf test?

[atuchin-m]

The result of CPU profiling of first 6 sec of browser process (Static local build, win-10, high-perf pc, VS studio profiler):
Total: 2914ms

Adblock:
783 Adblock lists parsing
30 OnDATLoaded
17 AdBlockFiltersProviderManager::FinishCombinating

Greaselion:
108 ConvertGreaselionRuleToExtensionOnTaskRunner
29 DeleteExtensionDirs

Wallet:
201 JSON data decoding callback, wallet/IPFS

HTTPS Everywhere:
182 Various SQLlite work

Chromium heavy stuff:
281 Safebrowsing (SHA256 database verification)
126 IsJoinedToAzureAD (check policy things?)
107 Session Restore

[atuchin-m]

About short-living processes:
we have about 7 instances of DataDecoderService during startup. They are likely to do (Wallet feature?) some JSON parsing work and it seems takes ~20-30ms per process (need to check)

[atuchin-m]

Related adblock work:
#33718
#33532

[atuchin-m]

DataDecoder issue: #30940

[atuchin-m]

Wallet startup performance (in case no created wallet): #33757

[atuchin-m]

other Wallet perf work:
#33758
#33759
#33760

[atuchin-m]

Greaselion old ticket about startup perf: #21366

[atuchin-m]

#34480

[atuchin-m]

Let's sum up the related work:

1. The Wallet problem was fixed: (Optimize json sanitizing in Wallet #30940).
2. The double adblock work on startup was fixed: ([perf] Fix double rebuilding of default ruleset #33718)
3. HTTP Everywhere was removed: Remove obsolete HTTPS Everywhere list from Brave since it's no longer needed #28433
4. Greaselion issue is open (no active maintainer)

That iteration of optimization for startup CPU usage can be considered as done.

[atuchin-m]

Another data-decoder issue: #35886
json parsing could be triggered during startup in several scenarios (e.g. when brave news is enabled).