Shader serialization experiment (with Mali Offline Compiler analysis)

1) Adds a --writeShaders option to fm. When that's included, the GPU
backend is run with a persistent cache (and no binary caching).
Then we dump all of the fragment shaders (GLSL for now) that were
created to the passed-in directory, along with a JSON digest listing
the number of times each one was referenced in the cache.

2) Adds a python script that invokes the Mali Offline Compiler on a
directory generated from #1, scraping the output of each compile for
cycle counts and writing the collated information to stdout.

Change-Id: Ie4b58ddac4f62e936707c6fec44f4fe605c213fa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206162
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed