Remove assumptions in get-selection-images web test.

The goal is that when we enable kEnableAccessibilityExposeHTMLElement,
relatively few tests will be affected. In this tests, there was
an assumption about nodes being an immediate child of the root element.

Bug: 1063155
Change-Id: I4b6388e5529e1b39cf67881b4830192363106b77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2206338
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772364}

third_party/blink/web_tests/accessibility/get-selection-images.html

@@ -9,7 +9,7 @@
   }
 </style>
 
-<img src="resources/cake.png" id="image1" alt="One"><img src="resources/cake.png" id="image2" alt="Two"><img src="resources/cake.png" id="image3" alt="Three">
+<div id="container"><img src="resources/cake.png" id="image1" alt="One"><img src="resources/cake.png" id="image2" alt="Two"><img src="resources/cake.png" id="image3" alt="Three"></div>
 
 <script>
   function setDOMSelection(anchorNode, anchorOffset, focusNode, focusOffset) {
@@ -29,10 +29,11 @@
 
   setup(() => {
     window.axRoot = accessibilityController.rootElement;
-    window.axBody = axRoot.childAtIndex(0);
+    window.axContainer = accessibilityController.accessibleElementById('container');
     window.axImage1 = accessibilityController.accessibleElementById('image1');
     window.axImage2 = accessibilityController.accessibleElementById('image2');
     window.axImage3 = accessibilityController.accessibleElementById('image3');
+    window.container = document.getElementById('container');
     window.image1 = document.querySelectorAll('img')[0];
     window.image2 = document.querySelectorAll('img')[1];
     window.image3 = document.querySelectorAll('img')[2];
@@ -54,28 +55,28 @@
   }, 'Test creating a selection around the first two images.');
 
   test(() => {
-    setDOMSelection(image1, 0, document.body, 3);
-    verifyAXSelection(axImage1, 0, axBody, 3);
+    setDOMSelection(image1, 0, container, 3);
+    verifyAXSelection(axImage1, 0, axContainer, 3);
   }, 'Test creating a selection around all the images.');
 
   test(() => {
-    setDOMSelection(document.body, 0, document.body, 0);
-    verifyAXSelection(axBody, 0, axBody, 0);
+    setDOMSelection(container, 0, container, 0);
+    verifyAXSelection(axContainer, 0, axContainer, 0);
   }, 'Test creating a collapsed selection before the first image from the body.');
 
   test(() => {
-    setDOMSelection(document.body, 0, document.body, 1);
-    verifyAXSelection(axBody, 0, axBody, 1);
+    setDOMSelection(container, 0, container, 1);
+    verifyAXSelection(axContainer, 0, axContainer, 1);
   }, 'Test creating a selection around the first image from the body.');
 
   test(() => {
-    setDOMSelection(document.body, 0, document.body, 2);
-    verifyAXSelection(axBody, 0, axBody, 2);
+    setDOMSelection(container, 0, container, 2);
+    verifyAXSelection(axContainer, 0, axContainer, 2);
   }, 'Test creating a selection before the first two images from the body.');
 
   test(() => {
-    setDOMSelection(document.body, 0, document.body, 3);
-    verifyAXSelection(axBody, 0, axBody, 3);
+    setDOMSelection(container, 0, container, 3);
+    verifyAXSelection(axContainer, 0, axContainer, 3);
   }, 'Test creating a selection around all the images from the body.');
 
   test(() => {
@@ -84,18 +85,18 @@
   }, 'Test creating a collapsed selection before the second image.');
 
   test(() => {
-    setDOMSelection(document.body, 1, document.body, 1);
-    verifyAXSelection(axBody, 1, axBody, 1);
+    setDOMSelection(container, 1, container, 1);
+    verifyAXSelection(axContainer, 1, axContainer, 1);
   }, 'Test creating a collapsed selection before the second image from the body.');
 
   test(() => {
-    setDOMSelection(image2, 0, document.body, 3);
-    verifyAXSelection(axImage2, 0, axBody, 3);
+    setDOMSelection(image2, 0, container, 3);
+    verifyAXSelection(axImage2, 0, axContainer, 3);
   }, 'Test creating a selection around the last two images.');
 
   test(() => {
-    setDOMSelection(document.body, 1, document.body, 3);
-    verifyAXSelection(axBody, 1, axBody, 3);
+    setDOMSelection(container, 1, container, 3);
+    verifyAXSelection(axContainer, 1, axContainer, 3);
   }, 'Test creating a selection around the last two images from the body.');
 
   test(() => {
@@ -104,12 +105,12 @@
   }, 'Test creating a collapsed selection before the third image.');
 
   test(() => {
-    setDOMSelection(document.body, 2, document.body, 2);
-    verifyAXSelection(axBody, 2, axBody, 2);
+    setDOMSelection(container, 2, container, 2);
+    verifyAXSelection(axContainer, 2, axContainer, 2);
   }, 'Test creating a collapsed selection before the third image from the body.');
 
   test(() => {
-    setDOMSelection(document.body, 3, document.body, 3);
-    verifyAXSelection(axBody, 3, axBody, 3);
+    setDOMSelection(container, 3, container, 3);
+    verifyAXSelection(axContainer, 3, axContainer, 3);
   }, 'Test creating a collapsed selection after the last image from the body.');
 </script>