Bump third_party/perfetto/repo from `b9aca8f` to `20ed12d` #2305

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	2m 19s
Build on Linux (gcc_debug)	2m 27s
Build on Darwin (clang, python_lib, simulated)	11m 44s
Build on Linux (coverage)	16m 28s
Build on Linux (python_lib)	2m 2s
Build on Linux (python lighting-app)	6m 26s
	41m 26s

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