Mitigate snapshot race in 3D transform test by reducing loop density - #193936

…lutter#193936)

Part of flutter#193689
Pre-requisite for flutter#192937

This PR reduces the angular sampling step in the 3D perspective
transform test to eliminate rapid snapshot cascades and stabilize the
`Mac framework_tests_impeller` shard.

While preparing flutter#192937, `Mac
framework_tests_impeller` failed repeatedly but not deterministically on
`3D transform renders the same with or without needsCompositing` in
`packages/flutter/test/widgets/transform_test.dart`. That PR recycles
the host buffer between snapshots to fix the memory leak. This test
takes back-to-back snapshots in a tight loop, which has an increased
likelihood of a GPU race condition when host buffers are recycled. The
chance of a problem increases with number of loop iterations, so this PR
just reduces the number of loops in `transform_test.dart` by increasing
the angle increment from `0.01` to `0.05`. I feel this still achieves
the purpose of the test while reducing flakiness related to host buffer
reuse.


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…density (flutter#196066)

Reverts: [Mitigate snapshot race in 3D transform test by reducing loop
density](flutter#193936)

Initiated by: @andywolff

Reason for reverting: not needed because
flutter#196063 is the true root cause
of the flakiness

Original PR Author: @andywolff

Reviewed By: @justinmc

The original PR description is provided below:

Part of flutter#193689
Pre-requisite for flutter#192937

This PR reduces the angular sampling step in the 3D perspective
transform test to eliminate rapid snapshot cascades and stabilize the
`Mac framework_tests_impeller` shard.

While preparing flutter#192937, `Mac
framework_tests_impeller` failed repeatedly but not deterministically on
`3D transform renders the same with or without needsCompositing` in
`packages/flutter/test/widgets/transform_test.dart`. That PR recycles
the host buffer between snapshots to fix the memory leak. This test
takes back-to-back snapshots in a tight loop, which has an increased
likelihood of a GPU race condition when host buffers are recycled. The
chance of a problem increases with number of loop iterations, so this PR
just reduces the number of loops in `transform_test.dart` by increasing
the angle increment from `0.01` to `0.05`. I feel this still achieves
the purpose of the test while reducing flakiness related to host buffer
reuse.


## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [AI contribution guidelines] and understand my
responsibilities, or I am not using AI tools.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant in-code documentation (doc comments with
`///`).
- [x] If this PR introduces a new feature or capability, I created and
linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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