One cause of the slowdown in issue 623661 is that static libraries strip code earlier in the link cycle than source_sets.
Binaries that depend on large portions of the build but don't depend on it means this earlier stripping makes a big performance impact. This is especially the case for test binaries in Chrome.
So we should try to make libraries that aren't required to be source sets static libraries in the GN build.
Comment 1 by bugdroid1@chromium.org
, Jul 13 2016