Reduces Safari's CanvasKit memory footprint for Flutter web apps while preserving platform-view composition.

Safari can retain a much higher physical footprint than Chrome for CanvasKit apps. In a production-style Flutter web flow with a Google Maps platform view, the baseline Safari WebContent footprint was 639.0M / 652.8M after 60 seconds idle, while Chrome stayed around 48.8M / 52.5M JS heap. This PR applies Safari-specific CanvasKit defaults, caps Safari's Skia resource cache, tightens web platform-view cleanup, and fixes an HtmlElementView create/dispose race.

Validation from the same flow after the change:

• Final Safari run through the normal bin/flutter web SDK cache: 373.0M / 451.8M after 60 seconds idle, with the map visible.
• Three cached Safari repeats: 383.87M / 443.63M mean after 60 seconds idle, with the map visible in all runs.
• Chrome guard through the normal SDK cache: 48.9M / 52.3M after 60 seconds idle, matching the baseline.

Fixes #93404

No flutter/tests migration is needed; this changes Flutter web engine and framework behavior without a breaking API change.

Release / cherry-pick information

Issue Link:

#93404

Impact Description:

Safari web apps using CanvasKit can use several hundred MB more memory than Chrome and may slow or crash. Apps using platform views, such as Google Maps, also need the Safari memory reduction to preserve underlay/overlay composition so the platform view remains visible.

Changelog Description:

[flutter/93404] When running CanvasKit Flutter web apps on Safari, reduce memory footprint with Safari-specific CanvasKit defaults while preserving platform-view composition.

Workaround:

Apps can manually set canvasKitForceCpuOnly: true and canvasKitMaximumSurfaces: 2, but this PR makes Safari defaults safer without requiring each app to configure them.

Risk:

• Low
• Medium
• High

Test Coverage:

• Yes
• No

Validation Steps:

• dart format engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/renderer.dart engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/surface.dart engine/src/flutter/lib/web_ui/lib/src/engine/compositing/rasterizer.dart engine/src/flutter/lib/web_ui/lib/src/engine/compositing/render_canvas.dart engine/src/flutter/lib/web_ui/lib/src/engine/compositing/surface.dart engine/src/flutter/lib/web_ui/lib/src/engine/configuration.dart engine/src/flutter/lib/web_ui/lib/src/engine/platform_views/content_manager.dart engine/src/flutter/lib/web_ui/test/canvaskit/rasterizer_test.dart engine/src/flutter/lib/web_ui/test/canvaskit/renderer_test.dart engine/src/flutter/lib/web_ui/test/engine/compositing/render_canvas_test.dart engine/src/flutter/lib/web_ui/test/engine/configuration_test.dart engine/src/flutter/lib/web_ui/test/engine/platform_views/content_manager_test.dart packages/flutter/lib/src/widgets/_html_element_view_web.dart packages/flutter/test/widgets/html_element_view_test.dart
• felt test --browser=chrome --renderer=canvaskit --suite=chrome-dart2js-canvaskit-engine --fail-early
• felt test --browser=chrome --renderer=canvaskit --suite=chrome-dart2js-canvaskit-canvaskit --fail-early
• flutter test --platform chrome test/widgets/html_element_view_test.dart
• git diff --check
• Manual Safari memory profile of the Rider web flow: home, trip options, and 60 seconds idle, including platform-view visibility checks.
• Chrome memory profile of the same flow as a regression guard.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

This is a draft until the submitter has completed human review of the AI-assisted changes and signed the CLA.