GitLab

1. Refactoring most of `AXRange::AsForwardRange` logic into a new static
   helper `CompareEndpoints` that determines between two `AXPosition`
   which one should be the start when using `AXRange::Iterator`.

   This helper is also used in `ITextRangeProvider::MoveEndpointByUnit`,
   in order to avoid more expensive comparisons of text positions.

2. As part of the `AsForwardRange` refactor, `CompareEndpoints` was
   optimized by avoiding even more text position comparisons.

3. Removing a pair of unnecessary calls to `CreateParentPosition` in
   `AXRange::GetScreenRects` when we iterate over inline text boxes.

   `CreateParentPosition` for a text position computes the max text
   offset of every subtree before the child node containing the given
   position, doing this sequentially for inline text boxes within the
   same parent node would result in n^2 calls to `MaxTextOffset`.

4. Before introducing these optimizations, the percentage of how much
   the subroutines above constituted a call to `GetScreenRects` were:

   AXRange::GetScreenRects                  Weight %
   |- AXPosition::CreateParentPosition       ~20.81%
   |- AXRange::Iterator::begin               ~18.28%
   |- AXRange::Iterator::end                 ~‭18.41%

   ITextRangeProvider::MoveEndpointByUnit   Weight %
   |- AXPosition::operator<                  ~10.01%‬

   After introducing this change's optimizations, the weight of every
   method listed was reduced to ~0% in their respective call stacks.

Bug: 928948
Change-Id: I0584e74af8327fdc3855a4d80060030998b7de95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1928320
Commit-Queue: Ethan Jimenez <ethavar@microsoft.com>
Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718411}