[canvaskit] Add profile mode

Firefox is the only browser that supports WASM+Source maps
so it's only really useful there.

It allows for profiling to see where time is speant, even
down in the C++ calls.  (see the below comment for a screenshot)

Bug: skia:
Change-Id: Ie0380bae9fdea45e1652dd7d2d8036f242087d33
Reviewed-on: https://skia-review.googlesource.com/c/174101
Reviewed-by: Mike Reed <reed@google.com>
2 files changed