A build mode where chrome.dll is split into two separate DLLs. This was undertaken as one possible workaround for toolchain limitations on Windows.
We removed support for this again after the toolchain limitations were fixed, see https://crbug.com/726150.
Split DLL used to be controlled by the is_multi_dll_chrome gn variable.
This forcible split was implemented by putting .lib files in either one DLL or the other, and causing unresolved externals that result during linking to be forcibly exported from the other DLL. This works relatively cleanly for function import/export, however it cannot work for data export.
Some more details can be found on the initial commit of the split_link script https://src.chromium.org/viewvc/chrome?revision=200049&view=revision and the associated bugs: https://crbug.com/237249 https://crbug.com/237267.