SuperSize has some pretty chromium-specific logic in it, but it's likely that you'll be able to use it somewhat at least.
Specifically, it parses build.ninja to find the list of input object files for the link step, and to map object file paths to source paths.
We try to keep it usable for non-chromium binaries, but that flow does tend to break from time to time. Happy to try and help fix things up if it doesn't work, but just warning that it may require some code tweaks.
So... that size, you should be able to get it to produce a minimal .size file given just a linker map file and an unstripped binary.
To get a linker map file, link with "-Wl,-Map=mylinker.map"
Then run the tool like:
tools/binary_size/supersize archive myfile.size --elf-file unstripped_binary --map-file mylinker.map --no-source-paths --tool-prefix=$CHROMIUM_SRC/third_party/android_ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/arm-linux-androideabi-
(you probably want to point the --tool-prefix to your copy of the ndk & for the correct architecture.
Final note - while the python code is mostly self-contained within //tools, there are dependencies outside of //tools. It will be easiest to just do a full chromium checkout (run "fetch android", where "fetch" is in depot_tools)