[patch][ccla] Reduce call stack in _ContentPaneResizeMixin#_layoutChildren

[Kenneth G. Franqueiro]

A customer identified a potential improvement to the _layoutChild method of _ContentPaneResizeMixin which has potential to significantly reduce the depth of call stacks (which can reduce memory consumption particularly in old IE).

The change involves changing from using array.forEach to using a straight for loop. Because the code in question is within _layoutChildren which is called by resize, this has potential to reduce the number of function calls not only on an individual ContentPane?, but also any nested ContentPanes? underneath.

Attaching a patch (under SitePen? CCLA). This patch was created from the 1.7 branch (since the customer is on 1.7), but will also cleanly apply to 1.8 and trunk.

[bill]

My guess is that

while(child = children[i++]){ ... }

would be even faster.

It's hard to believe either change is significant though, nor would I say that the change reduces recursion. But if it actually does reduce memory usage in a measurable way we should do it.

[Kenneth G. Franqueiro]

Yeah, your loop would probably work too.

The idea is that it no longer has to call forEach, nor would forEach perform additional calls to a callback, so it should be 2 fewer levels of recursion for each recursive level of ContentPane resizes.

Admittedly I was not able to see a noticeable performance difference myself (I tried, with a drastically unrealistic amount of nesting), and it's hard to really nail memory consumption since ostensibly memory would bounce back to normal the moment the resize operation completes.

[Kenneth G. Franqueiro]

After talking with Bill on IRC, I'm realizing that what I mean isn't technically reduced recursion, but reduced call stack depth. Changing title to hopefully clarify.

[bill]

OK, I'll switch it to a native loop in case it makes a difference.

[bill]

In [30679]:

use native loop instead of array.forEach() to fix alleged memory consumption issue in IE, fixes #16660 !strict