* Fixes resulting from audit of issues links
I looked at every link to GitHub in our repo. For cases where we had a TODO that was waiting for a bug to be fixed, and the bug has now been fixed, I applied the pending change. For cases where the link was out of date, I updated the link.
* Update run_test.dart
skip this test again since it failed on linux and macos bots
https://github.com/flutter/flutter/issues/17956
* Add a `debugInstrumentAction()` method that will wrap an action
in a stopwatch and print the time it took to run the action.
* Add a global `debugInstrumentationEnabled` that will control
whether `debugInstrumentAction()` does anything (even in debug
builds).
* Add some basic instrumentation to `registerServiceExtension()`
* Temporarily enable the `debugInstrumentationEnabled` flag in the
Gallery to give us better visibility into what's happening in
https://github.com/flutter/flutter/issues/17956
