Do not allow inert elements into the browser-side AX tree.

Bug: 996992
Change-Id: Ib36a9a42a97a27ed8fc4ad4f377abd49185a2e36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1814460Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Jacques Newman <janewman@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#699549}

content/test/data/accessibility/html/modal-dialog-opened-expected-android.txt

 android.webkit.WebView focusable scrollable
-++android.view.View
 ++android.app.Dialog role_description='dialog'
 ++++android.view.View name='The dialog subtree should be the only text content in the accessibility tree. '
 ++++android.view.View role_description='link' clickable focusable focused link name='Link inside the dialog.'
+++android.view.View

content/test/data/accessibility/html/modal-dialog-opened-expected-auralinux.txt

 [document web]
-++[section]
 ++[dialog] modal
 ++++[text] name='The dialog subtree should be the only text content in the accessibility tree. '
 ++++[link] name='Link inside the dialog.'
 ++++++[text] name='Link inside the dialog.'
+++[section]

content/test/data/accessibility/html/modal-dialog-opened-expected-blink.txt

 rootWebArea
-++genericContainer ignored invisible
-++++region ignored invisible
-++++++popUpButton collapsed ignored invisible value='This should be pruned out of the tree.'
-++++button ignored invisible name='Choose File' value='No file chosen'
-++genericContainer ignored invisible
-++dialog ignored invisible
-++genericContainer
 ++dialog
 ++++staticText name='The dialog subtree should be the only text content in the accessibility tree. '
 ++++++inlineTextBox name='The dialog subtree should be the only text content in the accessibility tree. '
 ++++link name='Link inside the dialog.'
 ++++++staticText name='Link inside the dialog.'
 ++++++++inlineTextBox name='Link inside the dialog.'
+++genericContainer

content/test/data/accessibility/html/modal-dialog-opened-expected-mac.txt

 AXWebArea
-++AXGroup
 ++AXGroup AXSubrole=AXApplicationDialog
 ++++AXStaticText AXValue='The dialog subtree should be the only text content in the accessibility tree. '
 ++++AXLink AXTitle='Link inside the dialog.'
 ++++++AXStaticText AXValue='Link inside the dialog.'
+++AXGroup

content/test/data/accessibility/html/modal-dialog-opened-expected-uia-win.txt

 document
-++group
 ++dialog Window.IsModal=true
 ++++description Name='The dialog subtree should be the only text content in the accessibility tree. '
 ++++link Name='Link inside the dialog.'
+++group

content/test/data/accessibility/html/modal-dialog-opened-expected-win.txt

 ROLE_SYSTEM_DOCUMENT READONLY FOCUSABLE
-++IA2_ROLE_SECTION
 ++ROLE_SYSTEM_DIALOG IA2_STATE_MODAL
 ++++ROLE_SYSTEM_STATICTEXT name='The dialog subtree should be the only text content in the accessibility tree. '
 ++++ROLE_SYSTEM_LINK name='Link inside the dialog.' FOCUSABLE
 ++++++ROLE_SYSTEM_STATICTEXT name='Link inside the dialog.'
+++IA2_ROLE_SECTION

content/test/data/accessibility/html/modal-dialog-stack-expected-android.txt

 android.webkit.WebView focusable focused scrollable
-++android.view.View
 ++android.app.Dialog role_description='dialog'
 ++++android.view.View name='This is the now active dialog. Of course it should be in the tree. '
 ++++android.widget.Button role_description='button' clickable focusable name='This is in the active dialog and should be in the tree.'
+++android.view.View

content/test/data/accessibility/html/modal-dialog-stack-expected-auralinux.txt

 [document web]
-++[section]
 ++[dialog] modal
 ++++[text] name='This is the now active dialog. Of course it should be in the tree. '
 ++++[push button] name='This is in the active dialog and should be in the tree.'
+++[section]

content/test/data/accessibility/html/modal-dialog-stack-expected-blink.txt

 rootWebArea
-++genericContainer ignored invisible
-++++region ignored invisible
-++++++popUpButton collapsed ignored invisible value='This should be pruned out of the tree.'
-++++button ignored invisible name='This button should not be in the tree.'
-++genericContainer ignored invisible
-++dialog ignored invisible
-++genericContainer
 ++dialog
 ++++staticText name='This is the now active dialog. Of course it should be in the tree. '
 ++++++inlineTextBox name='This is the now active dialog. Of course it should be in the tree. '
 ++++button name='This is in the active dialog and should be in the tree.'
+++genericContainer

content/test/data/accessibility/html/modal-dialog-stack-expected-mac.txt

 AXWebArea
-++AXGroup
 ++AXGroup AXSubrole=AXApplicationDialog
 ++++AXStaticText AXValue='This is the now active dialog. Of course it should be in the tree. '
 ++++AXButton AXTitle='This is in the active dialog and should be in the tree.'
+++AXGroup

content/test/data/accessibility/html/modal-dialog-stack-expected-uia-win.txt

 document
-++group
 ++dialog Window.IsModal=true
 ++++description Name='This is the now active dialog. Of course it should be in the tree. '
 ++++button Name='This is in the active dialog and should be in the tree.'
+++group

content/test/data/accessibility/html/modal-dialog-stack-expected-win.txt

 ROLE_SYSTEM_DOCUMENT READONLY FOCUSABLE
-++IA2_ROLE_SECTION
 ++ROLE_SYSTEM_DIALOG IA2_STATE_MODAL
 ++++ROLE_SYSTEM_STATICTEXT name='This is the now active dialog. Of course it should be in the tree. '
 ++++ROLE_SYSTEM_PUSHBUTTON name='This is in the active dialog and should be in the tree.' FOCUSABLE
+++IA2_ROLE_SECTION

third_party/blink/renderer/modules/accessibility/ax_object.cc

@@ -1211,6 +1211,11 @@ bool AXObject::ComputeAccessibilityIsIgnoredButIncludedInTree() const {
   if (!GetNode())
     return false;
 
+  // Disallow inert nodes from the tree to ensure the dialog is always the
+  // first child of the root.
+  if (GetNode()->IsInert())
+    return false;
+
   // If the node is part of the user agent shadow dom, or has the explicit
   // internal Role::kIgnored, they aren't interesting for paragraph navigation
   // or LabelledBy/DescribedBy relationships.