Disable CUA-irrelevant Chrome subsystems to reduce snapshot memory

[kalyazin]

Add startup flags to google-chrome.desktop that disable Chrome feature subsystems that serve no purpose in a computer-use-agent context. Security features (Safe Browsing, Site Isolation, phishing detection, WebAuthn, component updates, Privacy Sandbox) are deliberately left on because a single sandbox session may load multiple origins in tabs where one could be adversarial.

Measured on a Chrome-only bench build (ubuntu:22.04 + Xvfb + google-chrome-stable, no desktop environment; 3 browse cycles of 5 page navigations each). The absolute deltas are expected to carry over to the full desktop template as they are attributable solely to Chrome's own process memory.
snapshot memfile: −87 MB
snapshot rootfs: −42 MB
per-3-cycle memfile overhead: −49 MB
combined first-snapshot saving: ~129 MB

Flags added and rationale:

--disable-extensions
The extension system initialises a renderer and on-disk profile
directory even when no extensions are installed. CUA agents do not
use extensions.

--disable-default-apps
Skips the bundled "default app" install step (e.g. Chrome Web Store
shortcut, Docs, Sheets) that runs on first launch and writes to the
profile.

--disable-sync
Prevents the Chrome Sync service from starting. There is no Google
account in a sandbox; the service polls and writes to disk for
nothing.

--disable-spell-check
The Hunspell spell-checker loads dictionary files on startup.
Agents interact with pages programmatically and have no use for
in-browser spell checking.

--disable-breakpad
Disables the Breakpad crash reporter. The crash handler process and
its shared memory regions are unnecessary in a managed environment
where crashes are captured at the orchestrator level.

--metrics-recording-only --no-pings
Keeps Chrome's internal metrics counters working (so nothing crashes
expecting them) but disables all outbound UMA/UKM uploads and ping
traffic to Google servers.

--mute-audio
Prevents Chrome from opening an audio sink. There is no audio device
in the sandbox; without this flag Chrome still initialises the audio
subsystem and may log errors or spin waiting for a device.

--disable-features=Autofill,AutofillEnableUpi,PasswordManager,
FederatedCredentialsManagement
Autofill and the password manager scan every form field on every
page load, maintain an in-memory model, and write to the profile
database. Agents fill forms programmatically via xdotool/CDP.

--disable-features=InterestFeedContentSuggestions,PromotionalTabsEnabled
Prevents Chrome from fetching and storing content-suggestion feeds
and from opening promotional NTP tiles, both of which trigger
background network requests on startup.

--disable-features=Translate,TranslateUI,ReadAnything,DistilledPageContent
The translation and reading-mode subsystems watch every page load for
language signals and spin up background tasks. Agents read page
content via CDP or screenshot, not via Chrome's reader view.

--disable-features=PictureInPicture,Notifications
Picture-in-picture and the Notifications permission UI are human-
facing overlays that serve no purpose in a headless-style CUA session.

--disable-features=WebUSB,WebHID,WebMIDI,WebBluetooth,WebSerial,WebXR
Hardware-access APIs. There is no USB, HID, MIDI, Bluetooth, serial,
or XR device in the sandbox. Disabling them prevents Chrome from
enumerating device buses and registering device-arrival watchers.

--disable-features=MediaRouter,GlobalMediaControls,MediaSession
The Media Router (Chromecast/DIAL discovery), global media controls
overlay, and Media Session API all initialise background threads and
mDNS/SSDP listeners that are irrelevant without A/V playback or
casting targets.

--disable-features=PaymentRequest,Payments
The Payment Request API handler initialises the payments service and
loads payment-handler service workers on pages that include
payment-method metadata. No CUA workflow involves a payment flow.

--disable-features=WebRTC,WebRtcHWEncoding
WebRTC brings up the ICE agent, STUN/TURN resolution, and hardware
codec enumeration at browser start even when no page has called
getUserMedia or RTCPeerConnection. Absent microphone/camera devices
this is pure overhead.

--disable-features=BackgroundSync
A Service Worker API that queues "sync" events to be fired when
network connectivity is restored. Intended for offline-first apps
(e.g. sending a queued email after reconnecting). The sandbox is
always online and ephemeral; the sync queue machinery initialises
regardless.

--disable-features=BackgroundFetch
Extends BackgroundSync for large transfers that continue after all
tabs are closed. No CUA session needs multi-hour background downloads
that outlive the tab.

--disable-features=Push
The Web Push API. On subscribe, Chrome opens a persistent connection
to Google's FCM push service and can receive server-pushed messages
to wake a Service Worker even when the site is not open. The sandbox
has no push subscriptions and this is pure outbound noise.

--disable-features=Prerender2
Chrome's speculative pre-rendering: when confident the user will
navigate to a link, Chrome renders the destination in a hidden
background renderer process so the transition appears instant. A CUA
agent navigates programmatically and gains nothing from speculation;
the hidden renderer consumes a full process worth of memory for a
page the agent is about to load anyway.

[cursor]

PR Summary

Low Risk
Template-only launcher flag changes; security features are explicitly left enabled per PR description, with possible site-compat impact from disabled APIs.

Overview
Extends the Google Chrome desktop launcher Exec line with many startup flags aimed at computer-use-agent sandboxes: extensions, sync, spell-check, breakpad, outbound metrics pings (while keeping internal metrics), muted audio, and a long --disable-features= list (autofill/passwords, feeds, translate/reader, PiP/notifications, hardware APIs, media router/session, payments, WebRTC, background sync/fetch/push, prerender).

Also trims trailing whitespace on StartupWMClass=Google-chrome (no behavior change).

Intent: cut Chrome background work and memory on snapshots (~129 MB combined in bench per PR description) without turning off security-related subsystems called out in the PR body.

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