Enforce IWYU on ToolUtils.h

I plan to split this up to avoid #ifdefs in a follow-on CL

Bug: b/40045064
Change-Id: I84c918a9407faeb642d3b6c86cf1fe1105fa2e52
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/762402
Reviewed-by: Ben Wagner <bungeman@google.com>
15 files changed