Reland "VT: Remove containment requirement."

This reverts commit f2820f7b99c149d989dee94c1b23c791a7b5f387.

This was reverted earlier to wait for CSSWG feedback. The resolution
aligns with the behaviour in this patch.

w3c/csswg-drafts#8139

Original change's description:
> Revert "VT: Remove containment requirement."
>
> This reverts commit e554cf340761c4b11e0da4d0c98b1b58f9189cbd.
>
> Reason for revert: Decided against this feature for now.
>
> Original change's description:
> > VT: Remove containment requirement.
> >
> > This patch removes the containment requirement from view-transitions.
> >
> > This is to align with proposed resolution
> >  w3c/csswg-drafts#7882
> >
> > R=​khushalsagar@chromium.org, bokan@chromium.org
> >
> > Fixed: 1409491
> > Change-Id: Iad0eb54c8d2de503f209a58a9f438e586fcd6a36
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4188811
> > Reviewed-by: David Bokan <bokan@chromium.org>
> > Reviewed-by: Khushal Sagar <khushalsagar@chromium.org>
> > Commit-Queue: Vladimir Levin <vmpstr@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1096187}
>
> Change-Id: Id0b58230eb372a96aa1f1dff2e7d84e2f297219f
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4192788
> Commit-Queue: Vladimir Levin <vmpstr@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#1096273}

Change-Id: I3da1ee9d5e00b2a9470b99b5f69704fc9b4d0105
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4233087
Commit-Queue: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Khushal Sagar <khushalsagar@chromium.org>
Auto-Submit: Khushal Sagar <khushalsagar@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1102856}

css/css-view-transitions/3d-transform-incoming-ref.html

@@ -15,7 +15,6 @@
   background: blue;
 }
 .shared {
-  contain: layout;
   width: 100px;
   height: 100px;
 }

css/css-view-transitions/3d-transform-incoming.html

@@ -25,7 +25,6 @@
 }
 .shared {
   view-transition-name: shared;
-  contain: layout;
   width: 100px;
   height: 100px;
 }
@@ -34,7 +33,6 @@
   width: 10px;
   height: 10px;
   background: red;
-  contain: layout;
 }
 
 ::view-transition-group(hidden) { animation-duration: 300s; }

css/css-view-transitions/3d-transform-outgoing-ref.html

@@ -9,7 +9,6 @@
   background: green;
 }
 .shared {
-  contain: layout;
   width: 100px;
   height: 100px;
 }

css/css-view-transitions/3d-transform-outgoing.html

@@ -26,7 +26,6 @@
 }
 .shared {
   view-transition-name: shared;
-  contain: layout;
   width: 100px;
   height: 100px;
 }
@@ -35,7 +34,6 @@
   width: 10px;
   height: 10px;
   background: red;
-  contain: layout;
 }
 
 ::view-transition-group(hidden) { animation-duration: 300s; }

css/css-view-transitions/css-tags-paint-order-ref.html

@@ -5,7 +5,6 @@
 
 <style>
 div {
-  contain: layout;
   position: absolute;
   top: 50px;
   width: 100px;

css/css-view-transitions/css-tags-paint-order.html

@@ -7,7 +7,6 @@
 
 <script src="/common/reftest-wait.js"></script>
 <style>
-div { contain: layout; }
 #one {
   background: green;
   width: 100px;

css/css-view-transitions/dialog-in-top-layer-during-transition-new.html

@@ -17,8 +17,6 @@
   padding: 0;
 
   view-transition-name: dialog;
-  contain: layout;
-
   outline: none;
 }
 
@@ -28,7 +26,6 @@
   background: grey;
 
   view-transition-name: backdrop;
-  contain: layout;
 }
 
 .hidden {

css/css-view-transitions/dialog-in-top-layer-during-transition-old.html

@@ -17,8 +17,6 @@
   padding: 0;
 
   view-transition-name: dialog;
-  contain: layout;
-
   outline: none;
 }
 
@@ -28,7 +26,6 @@
   background: grey;
 
   view-transition-name: backdrop;
-  contain: layout;
 }
 
 .hidden {

css/css-view-transitions/element-with-overflow.html

@@ -12,14 +12,12 @@
     height: 10px;
     view-transition-name: hidden;
     background: green;
-    contain: layout;
   }
 
   .target {
     width: 100px;
     height: 100px;
     background: lightblue;
-    contain: layout;
     view-transition-name: target;
   }
   .inner {

css/css-view-transitions/named-element-with-fix-pos-child-new.html

@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html class=reftest-wait>
+<title>View transitions: element with fixed position descendant</title>
+<link rel="help" href="https://github.com/WICG/view-transitions">
+<link rel="author" href="mailto:khushalsagar@chromium.org">
+<link rel="match" href="named-element-with-fix-pos-child-ref.html">
+<script src="/common/reftest-wait.js"></script>
+<style>
+.target {
+  width: 100px;
+  height: 100px;
+  background: blue;
+  view-transition-name: target;
+}
+.child {
+  width: 100px;
+  height: 100px;
+  position: fixed;
+  top: 150px;
+  left: 150px;
+  background: grey;
+}
+
+html::view-transition-group(target) { animation-duration: 300s; }
+html::view-transition-old(target) { animation: unset; opacity: 0; }
+html::view-transition-new(target) {
+  animation: unset;
+  opacity: 1;
+}
+</style>
+
+<div class=target>
+  <div class=child></div>
+</div>
+
+<script>
+failIfNot(document.startViewTransition, "Missing document.startViewTransition");
+
+async function runTest() {
+  document.startViewTransition(() =>
+    requestAnimationFrame(() => requestAnimationFrame(takeScreenshot)));
+}
+onload = () => requestAnimationFrame(() => requestAnimationFrame(runTest));
+</script>
+

css/css-view-transitions/named-element-with-fix-pos-child-old.html

@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html class=reftest-wait>
+<title>View transitions: element with fixed position descendant</title>
+<link rel="help" href="https://github.com/WICG/view-transitions">
+<link rel="author" href="mailto:khushalsagar@chromium.org">
+<link rel="match" href="named-element-with-fix-pos-child-ref.html">
+<script src="/common/reftest-wait.js"></script>
+<style>
+.target {
+  width: 100px;
+  height: 100px;
+  background: blue;
+  view-transition-name: target;
+}
+.child {
+  width: 100px;
+  height: 100px;
+  position: fixed;
+  top: 150px;
+  left: 150px;
+  background: grey;
+}
+
+html::view-transition-group(target) { animation-duration: 300s; }
+html::view-transition-new(target) { animation: unset; opacity: 0; }
+html::view-transition-old(target) {
+  animation: unset;
+  opacity: 1;
+}
+</style>
+
+<div class=target>
+  <div class=child></div>
+</div>
+
+<script>
+failIfNot(document.startViewTransition, "Missing document.startViewTransition");
+
+async function runTest() {
+  document.startViewTransition(() =>
+    requestAnimationFrame(() => requestAnimationFrame(takeScreenshot)));
+}
+onload = () => requestAnimationFrame(() => requestAnimationFrame(runTest));
+</script>
+

css/css-view-transitions/named-element-with-fix-pos-child-ref.html

@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+<title>View transitions: element with fixed position descendant (ref)</title>
+<link rel="help" href="https://github.com/WICG/view-transitions">
+<link rel="author" href="mailto:khushalsagar@chromium.org">
+<style>
+.target {
+  width: 100px;
+  height: 100px;
+  background: blue;
+  view-transition-name: target;
+}
+.child {
+  width: 100px;
+  height: 100px;
+  position: fixed;
+  top: 150px;
+  left: 150px;
+  background: grey;
+}
+</style>
+
+<div class=target>
+  <div class=child></div>
+</div>
+

css/css-view-transitions/new-content-element-writing-modes.html

@@ -27,9 +27,6 @@
   contain: paint;
   border: 1px solid black;
 }
-.source {
-  contain: layout;
-}
 #target {
   background: red;
   position: absolute;

css/css-view-transitions/new-content-object-fit-fill.html

@@ -29,7 +29,6 @@
   width: 10px;
   height: 10px;
   view-transition-name: hidden;
-  contain: layout;
 }
 
 html::view-transition-group(target) {

css/css-view-transitions/new-content-object-fit-none.html

@@ -21,7 +21,6 @@
   width: 10px;
   height: 10px;
   view-transition-name: hidden;
-  contain: layout;
 }
 
 html::view-transition-group(target) {

css/css-view-transitions/old-content-object-fit-fill.html

@@ -29,7 +29,6 @@
   width: 10px;
   height: 10px;
   view-transition-name: hidden;
-  contain: layout;
 }
 
 html::view-transition-group(target) {