…position."

This reverts commit ed024d718b866ebc95f9eaed49a6c6dc546113d1.

Reason for revert: The original rationale that this would not change
any behavior without TransformInterop enabled was incorrect, because
backface-visibility: hidden (which does not create a containing block
for absolute/fixed) causes NeedsTransform() to be true, which thus
causes UpdateTransform to update rendering_context_id and
should_flatten_inherited_transform.

Original change's description:
> Make 3D Rendering Context follow DOM tree for absolute/fixed position.
>
> When TransformInterop is enabled, make the notion of 3D Rendering
> Context follow the DOM tree for absolute and fixed-positioned elements
> like it does for everything else.
>
> When TransformInterop is not enabled, there are no differences between
> following the DOM tree versus the containing block tree, which this
> DCHECK()s temporarily while storing the data in two places.  This is
> because the objects that changes of rendering_context_id and
> should_flatten_inherited_transform are associated with are all either
> containing blocks for absolute and fixed positioned elements or (for
> SVG) are associated closely enough with such containing blocks.
>
> (This is intended to change behavior only when
> RuntimeEnabledFeatures::TransformInteropEnabled(), though it should
> (once the temporary members are removed) unconditionally reduce the
> size of structs used on the stack.)
>
> Bug: 1189985
> Change-Id: I5d3bff009e2fbac00d3d011a6a9adc77ad2f9829
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2776711
> Reviewed-by: Philip Rogers <pdr@chromium.org>
> Commit-Queue: David Baron <dbaron@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#878158}

Bug: 1189985
Fixed: 1204790, 1204853
Change-Id: Idb2a635edd9b762454bb23c536cb37bc2ac7330f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2873105
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: David Baron <dbaron@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#879166}