tree c6f57b84e92eb9faf31a80c9b576cdab3f54608d
parent ab4c24db99dce640d880737f55ca7f770786aa14
author Ben Rohlfs <brohlfs@google.com> 1652863579 +0200
committer Ben Rohlfs <brohlfs@google.com> 1653050399 +0200

Fix events emitted by gr-diff-builder-element

We had multiple issues with render-* events.

Change 334544 has added a 'render-progress' event for updating cursor
stops while the rendering is still in progress. This has now been
identified as substantially impacting rendering performance. Such events
were fired hundreds of times per second (one for each diff group).
Updating cursor stops involves querying the DOM, which forces the
browser to reflow. This should be avoided, so we are removing
'render-progress' events altogether in this change. Maybe a solution for
updating cursor stops is using a timer that fires every 500 ms or so.
But that needs some careful thought and has to be done in a separate
change.

Change 336092 tried to fire 'render-*' events only after DOM rendering
has completed, but it did not work as intended, and change 336494 tried
to fix that. But it turns out that `afterNextRender` uses
`requestAnimationFrame`, which is not invoking callbacks while tabs are
in the background. This broke Gerrit's latency metrics and triggered
SLO alerts, see b/232095724. We are replacing usages of
`afterNextRender` by `whenRendered`, which is using a `ResizeObserver`
and waits for the DOM element to get a clientHeight > 0.

Google-Bug-Id: b/232095724
Release-Notes: skip
Change-Id: I98d99ca43bf12ba901bb2defe8a4ded3bf0f587c