Specify CPU for CT Swarming tasks.

This ensures we are doing apples-to-apples comparison across runs.

The Chrome-GPU pool has different machines with the same GPU, so it's
important to lock down to a specific CPU for perf testing.

No-Try: true
Change-Id: I66648c4ea58b835af0a63d36f4830b26d7c65c5f
Reviewed-on: https://skia-review.googlesource.com/50760
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
13 files changed