Revert "Default navigation in VoiceOver includes only visible elements"

This reverts commit 763fd8b4.

Reason for revert: Broke VoiceOver navigation by heading, link, etc. when the object in question is scroll off the screen.

Original change's description:
> Default navigation in VoiceOver includes only visible elements
> 
> Navigation with the VO cursor should not visit hidden elements.
> This had regressed because we started including hidden elements
> in the accessible object hierarchy on purpose, so that when
> a page accidentally overused aria-hidden, that users would
> still hear something useful when tabbing to focusable items.
> With this CL, users will not generally be able to accidentally
> navigate to aria-hidden items, but if they manage to actually
> focus one with the keyboard, it will still announce what it is.
> 
> Bug: 982408
> Change-Id: I19d5fe4947e5fb1c7493f0e67d7fe8e13d9a255e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1761717
> Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
> Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#689677}

TBR=aboxhall@chromium.org,aleventhal@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 982408
Change-Id: I3242ac4dc633d557a8ddc1d4125fbdfdd7990720
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846180Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703966}

content/browser/accessibility/browser_accessibility_cocoa.mm

@@ -607,7 +607,7 @@ bool InitializeAccessibilityTreeSearch(OneShotAccessibilityTreeSearch* search,
   if ([immediateDescendantsOnlyParameter isKindOfClass:[NSNumber class]])
     immediateDescendantsOnly = [immediateDescendantsOnlyParameter boolValue];
 
-  bool visibleOnly = true;  // Default to visible only.
+  bool visibleOnly = false;
   NSNumber* visibleOnlyParameter = [dictionary objectForKey:@"AXVisibleOnly"];
   if ([visibleOnlyParameter isKindOfClass:[NSNumber class]])
     visibleOnly = [visibleOnlyParameter boolValue];