Building MD Settings only executes 14 targets and is fairly fast (with use_vulcanize = false). On the other hand, building MD History and MD Downloads executes 64 targets each, some of which seem fairly unrelated.

Pasting below, but also see screencast.

~/workspace/chromium1/src > touch chrome/browser/resources/settings/settings.html 
~/workspace/chromium1/src > ninja -C out/gchrome_gn/ chrome -j200 -l50
ninja: Entering directory `out/gchrome_gn/'
[14/14] STAMP obj/chrome/packed_resources.stamp
~/workspace/chromium1/src > touch chrome/browser/resources/md_history/history.html 
~/workspace/chromium1/src > ninja -C out/gchrome_gn/ chrome -j200 -l50
ninja: Entering directory `out/gchrome_gn/'
[64/64] LINK ./chrome
~/workspace/chromium1/src > touch chrome/browser/resources/md_downloads/downloads.html 
~/workspace/chromium1/src > ninja -C out/gchrome_gn/ chrome -j200 -l50
ninja: Entering directory `out/gchrome_gn/'
[64/64] LINK ./chrome


I believe this is happening because MD Settings declares all its resources in its own grd file [1], whereas History and Downloads re-use the global browser_resources.grd [2] and [3] respectively.

[1] https://cs.chromium.org/chromium/src/chrome/browser/resources/settings/settings_resources.grd
[2] https://cs.chromium.org/chromium/src/chrome/browser/browser_resources.grd?l=299
[3] https://cs.chromium.org/chromium/src/chrome/browser/browser_resources.grd?l=151-174
 

Deleted: slow_build.mp4 553 KB

	slow_build.mp4 553 KB View Download