Original change's description:
> Switch on building devtools from source when building the Dart SDK
>
> Fixes https://github.com/flutter/devtools/issues/9786 >
> See go/moving-devtools-to-dart-sdk-2025.
>
> In this change, we make the source of devtools be configurable, in
> actions like build_sdk.
>
> If `build_devtools_from_sources` is true, we build local devtools,
> and if false, we continue to use the prebuilt sources.
>
> This may be an intermediate step, while we test out building devtools
> from source. Or it may be permanently be a choice, if we keep building
> with CIPD.
>
> Change-Id: I7b46d6359c69b34f316e59dccc475e211a18f965
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/498640 > Reviewed-by: Alexander Aprelev <a...@google.com>
> Commit-Queue: Samuel Rawlins <sraw...@google.com>