Reland "innerText setter should not modify an existing Text child"

This reverts commit 43e1f5d7d3d80071dc0bc9f65bf34be770c250c1.

Reason for revert: Revert didn't fix the flaky test, reland the CL.

Original change's description:
> Revert "innerText setter should not modify an existing Text child"
> 
> This reverts commit 976ec7a98c98b707e9b5bd73c515069b2e0d5cbb.
> 
> Reason for revert: crbug.com/938591
> 
> Original change's description:
> > innerText setter should not modify an existing Text child
> > 
> > We have an optimization reusing a Text child, but the standard doesn't
> > define such behavior, and Edge, Firefox, and Safari don't have it.
> > 
> > This CL might regress benchmarks.  We'll accept it.
> > 
> > Bug: 573309
> > Change-Id: I3aacae5d37e5a7685ce2d310944dfef8d6e4b13a
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1502338
> > Commit-Queue: Kent Tamura <tkent@chromium.org>
> > Auto-Submit: Kent Tamura <tkent@chromium.org>
> > Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#637665}
> 
> TBR=yosin@chromium.org,tkent@chromium.org
> 
> Change-Id: Ib1884d8b20d9c8d10fc1566498cbdd719cc97b50
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 573309
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504128
> Reviewed-by: Owen Min <zmin@chromium.org>
> Commit-Queue: Owen Min <zmin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#637805}

TBR=yosin@chromium.org,tkent@chromium.org,zmin@chromium.org

Change-Id: Id66ace389fd1b318b57b598e462182155a5f9d0b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 573309
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1505997
Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638126}
13 files changed