Add extra flags to disable throttling behavior. (#55)

* Add extra flags to disabling throttling behavior.

These flags [were added in our internal SDK test infrastructure][1] and they
helped reduce flaky timeout behavior in the past. It's very likely that
these and the `--disable-background-timer-throttling` flag that's
already here have some overlap, though.

I have not been able to find much documentation about whether they do
overlap, so I was inclined to try to add these by default and
assess the effect in our CI.

[1]: https://dart-review.googlesource.com/c/sdk/+/325780/2/pkg/test_runner/lib/src/browser_controller.dart

* ... add CHANGELOG

CHANGELOG.md

@@ -3,6 +3,7 @@
 - Require Dart 3.0
 - Log errors from chrome
 - Allow tests to detect headless-only environment (for CI).
+- Add extra flags that may help disable additional throttling in background tabs
 
 ## 1.1.1
 

lib/src/chrome.dart

@@ -102,6 +102,8 @@ class Chrome {
       '--remote-debugging-port=$port',
       // When the DevTools has focus we don't want to slow down the application.
       '--disable-background-timer-throttling',
+      '--disable-blink-features=TimerThrottlingForBackgroundTabs',
+      '--disable-features=IntensiveWakeUpThrottling',
       // Since we are using a temp profile, disable features that slow the
       // Chrome launch.
       if (!signIn) '--disable-extensions',