Add new task to run the float-cast-overflow sanitizer.

Bug: skia:4632
No-Try: true
Change-Id: I85a0b23037d5885e5d762788d8bf5b7cc6fc19b2
Reviewed-on: https://skia-review.googlesource.com/45980
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
10 files changed