Changing a central header file in core/layout/ (such as LayoutObject.h or LayoutBlockFlow.h) and rebuilding just gets slower and slower as the months go by.
Eliminating unnecessary includes and making some light changes suggests that we can improve the speed by at least 38%.
Changing and recompiling LayoutObject.h should now be ~38% faster. Closing.
I tried to make some further and crazy changes, such as not including ComputedStyle.h and Document.h from LayoutObject.h, but it only seemed to make it about 3% faster. So probably not worth it, given all the mess it required.
Comment 1 by japhet@chromium.org
, May 23 2016