Hi Peter:
Thanks for the doc, configuring clang_base_path and adding the sanitizer options (-fsanitize=) to the toolchain.ninja are exactly the thing I did, there are a few troubles regarding flatc, cddl, protobuf, and some generators (returns error status -11, etc).
I have written a bin/sh wrapper not to instrument c/c++ code under those submodules as I think the final chrome would not contain any code from those third party tools. But please let me know if you think this is incorrect.
I'm also studying how to deploy the sanitizer from asan, if the previous approach fails, I would deploy the customized sanitizer as what asan did. It seems it needs to modify some configuration files(.gn or .gni as you pointed) to set up the sanitizer option and add some flags.