Creating a lot of nsDisplayCompositorHitTestInfo items is expensive, and currently we always create one for stacking contexts. These patches carry the hit test information in stacking context container items instead.

Depends on D10130

Depends on D10131

These patches introduce HitTestInfo struct, which contains the information needed to accumulate hit test area and flags into PaintedLayerData, and nsDisplayHitTestInfoItem, which is a base class for display items that can carry compositor hit test info. The new base class is introduced to avoid increasing memory footprint of all display items, and to avoid duplicating code. The basic idea is the following: - When building a display list for a stacking context, a HitTestInfo struct is created with the same information that nsDisplayCompositorHitTestInfo would have been created with. - This HitTestInfo is added to the innermost container item that was created for the stacking context frame. If no container item was created, a nsDisplayCompositorHitTestInfo item is created instead. - When FLBDisplayItemIterator processed a container item, DisplayItemEntry with a type HIT_TEST_INFO is emitted with the item set to the container item. Extra care is needed here because of the different flattening methods: for opacity and transforms we need to place the HIT_TEST_INFO marker in between the flattened effect markers, and for other container items before any other child items.

Pushed by mikokm@gmail.com: https://hg.mozilla.org/integration/autoland/rev/7afff3818ad7 Part 1: Add simple hit test info diagnostics r=mattwoodrow https://hg.mozilla.org/integration/autoland/rev/b4c35701070b Part 2: Introduce HitTestInfo and nsDisplayHitTestInfoItem, and make container items and nsDisplayCompositorHitTestInfo use them r=mattwoodrow https://hg.mozilla.org/integration/autoland/rev/4408e5678aa6 Part 3: Generalize FrameLayerBuilder hit test info handling r=mattwoodrow

https://hg.mozilla.org/mozilla-central/rev/7afff3818ad7 https://hg.mozilla.org/mozilla-central/rev/b4c35701070b https://hg.mozilla.org/mozilla-central/rev/4408e5678aa6

performance improvements: == Change summary for alert #17337 (as of Fri, 02 Nov 2018 06:23:36 GMT) == Improvements: 11% displaylist_mutate windows7-32 pgo e10s stylo 2,130.61 -> 1,898.68 11% displaylist_mutate windows10-64 pgo e10s stylo 2,048.11 -> 1,827.78 10% displaylist_mutate linux64 opt e10s stylo 2,037.21 -> 1,826.33 10% displaylist_mutate windows7-32 opt e10s stylo 2,240.34 -> 2,021.39 9% displaylist_mutate linux64 pgo e10s stylo 1,884.15 -> 1,708.80 9% displaylist_mutate windows10-64 opt e10s stylo 2,156.55 -> 1,956.80 9% displaylist_mutate osx-10-10 opt e10s stylo 5,280.09 -> 4,805.19 For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=17337