Removes workaround for autofill popups from AXPosition

After https://crrev.com/c/2122718 has landed
which switches to using inner text instead of the kValue
attribute for retrieving the contents of text fields
in AXPosition, there is no longer a need to have a workaround for
computing the parent position of a text position that is
located inside an autofill popup that is a child
of a text field, since the text of the
popup, i.e. the autofill suggestion, would be part of inner text/.
Previously, the kValue attribute didn't reflect the value of any autofill suggestion.

RelNotes: Users of VoiceOver, NVDA and Jaws screen readers are able to use the
"Read Current Line" and "Read Current Word" commands to read the placeholder text in a text field.
<label>Name: <input type="text" placeholder="John Doe"></label>

R=dmazzoni@chromium.org, aleventhal@chromium.org

Change-Id: If57e012e8d16fa2b99e091aa5f86a0f145e266d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2125450Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Auto-Submit: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754524}

content/browser/accessibility/browser_accessibility_unittest.cc

@@ -743,14 +743,20 @@ TEST_F(BrowserAccessibilityTest, NextWordPositionWithHypertext) {
   auto position = input_accessible->CreatePositionAt(
       0, ax::mojom::TextAffinity::kDownstream);
 
-  // On platforms that expose IA2 or ATK hypertext, moving by word should have
-  // no effect, i.e. return the same position, since the visible text is just a
-  // placeholder and should not appear in the input field's hypertext.
+  // On platforms that expose IA2 or ATK hypertext, moving by word should work
+  // the same as if the value of the text field is equal to the placeholder
+  // text.
+  //
+  // This is because visually the placeholder text appears in the text field in
+  // the same location as its value, and the user should be able to read it
+  // using standard screen reader commands, such as "read current word" and
+  // "read current line". Only once the user starts typing should the
+  // placeholder disappear.
+
   auto next_word_start = position->CreateNextWordStartPosition(
       ui::AXBoundaryBehavior::CrossBoundary);
-  ASSERT_TRUE(next_word_start->IsTextPosition());
   if (position->MaxTextOffset() == 0) {
-    EXPECT_EQ(*position, *next_word_start);
+    EXPECT_TRUE(next_word_start->IsNullPosition());
   } else {
     EXPECT_EQ(
         "TextPosition anchor_id=2 text_offset=7 affinity=downstream "
@@ -760,9 +766,8 @@ TEST_F(BrowserAccessibilityTest, NextWordPositionWithHypertext) {
 
   auto next_word_end = position->CreateNextWordEndPosition(
       ui::AXBoundaryBehavior::CrossBoundary);
-  ASSERT_TRUE(next_word_end->IsTextPosition());
   if (position->MaxTextOffset() == 0) {
-    EXPECT_EQ(*position, *next_word_end);
+    EXPECT_TRUE(next_word_end->IsNullPosition());
   } else {
     EXPECT_EQ(
         "TextPosition anchor_id=2 text_offset=6 affinity=downstream "

ui/accessibility/ax_position.h

@@ -1093,11 +1093,13 @@ class AXPosition {
       return copy;
     }
 
-    // Blink doesn't always remove all deleted whitespace at the end of a
-    // textarea even though it will have adjusted its value attribute, because
-    // the extra layout objects are invisible. Therefore, we will stop at the
-    // last child that we can reach with the current text offset and ignore any
-    // remaining children.
+    // We stop at the last child that we can reach with the current text offset
+    // and ignore any remaining children. This is for defensive programming
+    // purposes, in case "MaxTextOffset" doesn't match the total length of all
+    // our children. This may happen if, for example, there is a bug in the
+    // internal accessibility tree we get from the renderer. In contrast, the
+    // current offset could not be greater than the length of all our children
+    // because the position would have been invalid.
     int current_offset = 0;
     int child_index = 0;
     for (; child_index < copy->AnchorChildCount(); ++child_index) {
@@ -1827,18 +1829,6 @@ class AXPosition {
 
         AXPositionInstance parent_position = CreateTextPosition(
             tree_id, parent_id, parent_offset, parent_affinity);
-        if (parent_position->IsNullPosition()) {
-          // Workaround: When the autofill feature populates a text field, it
-          // doesn't immediately update its value, which causes the text inside
-          // the user-agent shadow DOM to be different than the text in the text
-          // field itself. As a result, the parent_offset calculated above might
-          // appear to be temporarily invalid.
-          // TODO(nektar): Fix this better by ensuring that the text field's
-          // hypertext is always kept up to date.
-          parent_position =
-              CreateTextPosition(tree_id, parent_id, 0 /* text_offset */,
-                                 ax::mojom::TextAffinity::kDownstream);
-        }
 
         // If the current position is pointing at the end of its anchor, we need
         // to check if the parent position has introduced ambiguity as to