Restructured code to reduce the number of allocations during dispatch.

[nirvdrum]

I use Tree Style Tab with a fairly large number of tabs. I love the extension, but it causes my battery to drain too quickly. I'm sure at a lower number of tabs, this isn't much of a problem. But, I'm profiling it now and trying to fix some stuff.

This set of changes is fairly small, but cuts the retained memory for 18% -> 3% and the allocated memory from 8% -> 2% when I profiled with 25 tabs. I tried to profile under similar conditions and I only focused on "Web Extensions" in the profiler, but there are system variances and workload variances that likely impact it. I ran the profiles multiple times and got similar results each time. But, I'd still take the absolute numbers with a grain of salt and focus more on the relative difference between them. While I didn't focus explicitly on it, it appears from the profiles that GC frequency dropped as well.

The summary of changes are:

• Eagerly allocate the results array with the correct size to avoid any array resizes
• Instead of cloning the set of listeners just to map over the array, iterate over the set directly
  • I'm assuming either the iteration order doesn't matter or that the system will consistently iterate over a set the same way it would construct an array from a set. If iteration order is important, we should rethink storing the listeners as a set in the first place
  • This eliminates the array allocation and the data copy
  • This eliminates the allocation of the anonymous function passed to the map call

While I realize this changes from a functional style to a more procedural style, the performance impact is fairly large. I'm open to other approaches as well. I profiled keeping the map but hoisting the function passed to it so we can just pass a function reference rather an allocate a function object. That helps as well and maybe makes the code a bit cleaner, but the benefit was only about half of what this PR proposes.

[piroor]

Thank you for investigation! I agree that my codes are often not optimized well, so optimizations are always welcome for me.

I'll merge this after the first needless part is reverted.

[piroor]

Thanks a lot! I'll update depender addons ASAP.