Add Flutter compile bot

BUG=skia:6227

Change-Id: I997663e49c407e3ec64c8e67a2ca27700d5081b4
Reviewed-on: https://skia-review.googlesource.com/8448
Commit-Queue: Ravi Mistry <rmistry@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
9 files changed