[Nit] Fixes include lint in dart_tools_api.h
[Nit] Fixes include lint in dart_tools_api.h

Fixes:
"dart_tools_api.h:8:  Include the directory when naming .h files .."

Change-Id: Ie22fb13a031328c02b01a0708674761d27659d10
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/160064
Commit-Queue: Clement Skau <495593248b6158163719b90dde8357b589c8e5d0@google.com>
Reviewed-by: Aske Simon Christensen <589eb3fd9a84f06d0ac46d3aa71dddcfb0814ccd@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk