This is the argument that resonates with me the most. Unless you're already intimately familiar with the codebase and build system (with all their attendant quirks), it could consume a huge amount of time and effort to tease apart the stuff you need from the vast chromium codebase.
For the record, I'm working on a new C++ project where I ended up picking up small (very small) pieces of chromium codebase with the rest being in conservatively written C++ (but not as conservative as described in google code-style guide). In general, I'd say /base and /threading libraries are useful sources to raid at the beginning of your project. These are high quality implementations of basic things most programs would need and somewhat easier to disentangle from the rest of the code.
i think theres a safe threshold someone can use as a rule, before things get too much complicated..
first: know how to use gyp and ninja build tools
then.. you can embed: base, crypto, net and ipc..
Anything more than that, things start to get more complicated.. for instance: if you want to use the 'ui'.. then you have to embed 'cc' and 'gpu'.. and to work right.. you will need the browser process + the gpu process.. and will have to create a custom-renderer, or adapt the renderer process to yourself.. so now you will realize you are doomed!
The other Chrome components past the ones i've pointed out, will need to use the IPC and multiprocess logic from chrome.. so that part should only be used in very specific scenarios..
Edit: i think the 'cc' module, the chrome compositor, also has some sort of autonomy from the multiprocess IPC core.. so could also be used with: base, crypto, net and ipc
For the record, I'm working on a new C++ project where I ended up picking up small (very small) pieces of chromium codebase with the rest being in conservatively written C++ (but not as conservative as described in google code-style guide). In general, I'd say /base and /threading libraries are useful sources to raid at the beginning of your project. These are high quality implementations of basic things most programs would need and somewhat easier to disentangle from the rest of the code.