Framework web tests take too long to run.

Example: https://ci.chromium.org/ui/p/flutter/builders/luci.flutter.prod/Linux%20web_canvaskit_tests_7_last. This is one of 8 shards running framework tests against CanvasKit. It's consistently taking 30+ minutes!

Some ideas for improvement:

• Reuse the same Chrome instance for all test suites:
  • [web] Reuse chrome instance to run all flutter tests #174957
• Run all test suites within the same iframe (may lead to unintended leaks across tests).
• Compile with dart2js instead of DDC.
• Run Skwasm tests in fewer shards to minimize overhead.
  • Run skwasm framework unit tests on a single shard. #175001
  • [web] Reduce Skwasm test shards to 2 #178239