ArrayList/ArrayCollection performance improvements

Considerable performance gains can be achieved by avoiding the use of array splice when adding/removing items from the start or end of the source array in ArrayList.

eg/ in ArrayList.addItemAt, replace this:

source.splice(index, 0, item);

with this:

 
if (index == length)
    source.push(item);
else if (index == 0)
    source.unshift(item);
else
    source.splice(index, 0, item);

ArrayList.addItem is 10x faster when adding non IEventDispatcher's, and 6x faster for IEventDispatcher's. There is a small trade-off when performing random access add/removes, where the extra logic slightly increases the times taken.

Since ArrayCollection wraps an ArrayList by default and ArrayCollection.addItem is used extensively within our apps, this patch has provided considerable performance improvements.

See profiling results below:

Original ArrayList, adding/removing 100k ints

• addItemAtStart = "2434ms"
• addItemAtEnd = "2501ms"
• addItemAtRandom = "3149ms"
• removeItemAtStart = "3098ms"
• removeItemAtEnd = "2401ms"
• removeItemAtRandom = "2606ms"

Original ArrayList, adding/removing 100k IEventDispatcher's

• addItemAtStart = "2501ms"
• addItemAtEnd = "2505ms"
• addItemAtRandom = "3165ms"
• removeItemAtStart = "3053ms"
• removeItemAtEnd = "2453ms"
• removeItemAtRandom = "2709ms"

Patched ArrayList, adding/removing 100k ints

• addItemAtStart = "226ms"
• addItemAtEnd = "213ms"
• addItemAtRandom = "3281ms"
• removeItemAtStart = "803ms"
• removeItemAtEnd = "219ms"
• removeItemAtRandom = "2808ms"

Patched ArrayList, adding/removing 100k IEventDispatcher's

• addItemAtStart = "415ms"
• addItemAtEnd = "488ms"
• addItemAtRandom = "3662ms"
• removeItemAtStart = "878ms"
• removeItemAtEnd = "264ms"
• removeItemAtRandom = "2949ms"