The file
src/3rdparty/chromium/third_party/blink/manual_tests/WebKitSite.webarchive
is an archive of a web page containing nonfree Javascript. Using
pywebarchive to extract it, one finds the nonfree file urchin.js (from
Google Analytics).

Besides that, there are some pre-built binaries:

src/3rdparty/chromium/third_party/vulkan-deps/glslang/src/Test/*.spv
src/3rdparty/chromium/third_party/jni_zero/samples/java/src/org/jni_zero/samples/JavapClass.class
src/3rdparty/chromium/third_party/angle/third_party/r8/custom_d8.jar
src/3rdparty/chromium/third_party/beto-core/src/nearby/connections/ukey2/ukey2_jni/java/gradle/wrapper/gradle-wrapper.jar
src/3rdparty/chromium/third_party/beto-core/src/nearby/presence/ldt_np_jni/java/LdtNpJni/gradle/wrapper/gradle-wrapper.jar
src/3rdparty/chromium/third_party/libavif/src/android_jni/gradle/wrapper/gradle-wrapper.jar
src/3rdparty/chromium/third_party/libwebp/src/gradle/wrapper/gradle-wrapper.jar
src/3rdparty/chromium/third_party/libwebp/src/swig/libwebp.jar
src/3rdparty/chromium/third_party/r8/custom_d8.jar

Based on this being included in a directory named  “samples”, this could probably be
excluded without any loss of functionality.

This could probably be excluded if the package were to build-depend on libavif-dev and
the code were patched to use it.

This can probably be excluded, as the package already build-depends on libwebp-dev.

The rest of these will take some investigation.

I will probably end up splitting this bug report into multiple different bugs as each one
could require different solutions.

Control: block -1 by 1091463
This has been split off into:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1091463