Add a fast-path for independent inherited properties
Add a fast-path for inherited properties which do not depend on and do
not affect any other properties on ComputedStyle. When these properties
are modified in a parent element, set them directly on ComputedStyle and
skip doing a full recalc for elements only affected by this change.
Also implemented two of these properties: visibility and pointer-events,
storing an extra 2 bits per ComputedStyle. This increases the size of
ComputedStyle by 1 byte on Windows and some Android builds (due to
aligned fields), which increases the memory usage for a standard page
with ~1000 elements by up to 1kb (although potentially up to 4/8kb on
32/64 bit builds due to packing, although this depends on the allocator
implementation details) but realistically less since style sharing only
creates one ComputedStyle object for each unique style.
Benchmarks show a speed increase of up to 2x for setting these
properties on the root element of a typical web page (Facebook, Twitter,
Pinterest, Amazon, Wikipedia) and letting the change propagate directly
onto the child ComputedStyle objects, rather than doing a full style
recalc.
Initial Benchmarks:
https://docs.google.com/spreadsheets/d/1mUuJEs8cPWyNTR7tQw27oxq6fDTvWiAwgatf_g--B4w/edit#gid=1597242813
Follow-up Benchmarks:
https://docs.google.com/spreadsheets/d/1mUuJEs8cPWyNTR7tQw27oxq6fDTvWiAwgatf_g--B4w/edit#gid=918856082
BUG=622138
Review-Url: https://codereview.chromium.org/2117143003
Cr-Commit-Position: refs/heads/master@{#409143}
15 files changed
