Address comment in https://github.com/flutter/flutter/pull/66386/files#r522671103

Due to #69707 the SkSL tests need the process killing logic still.

This reverts commit 406ca0bc.

My yearly pass to fix spelling errors in the API dartdocs.

* [devicelab] work around occasional null values for devtools

* Update perf_tests.dart

Rolls in several fixes to web tooling, including better handling of absolute file imports. Updates to latest vm service to unblock null safety mode query
Co-authored-by: Gary Roumanis <grouma@google.com>
Co-authored-by: Anna Gringauze <annagrin@google.com>

* update pinned null safety deps

* run update-packages

* add http dep to devicelab package

* rerun update-packages

* [devicelab] mark uncaight exceptions as flaky

* add print error output

* try and fix test

* [flutter_tools] remove iOS screenshot on failure functionality

* remove all screenshot code