Introduced const correctness in ViewAccessibility::Next/PreviousFocus methods

Once a getter method is not marked const, it could force other parts of the codebase to drop const as well, requiring a larger refactoring to fix in the future.
Also took the opportunity to add a comment describing the related member variables
and clarify some other comments.

Split out from a larger patch dealing with ignored Views.

AX-Relnotes: n/a.

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

Change-Id: Ic7c4f6d38f83ef2a22401b0edd342cef5f61c58c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2581220Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835348}

ui/views/accessibility/view_accessibility.cc

@@ -255,7 +255,7 @@ void ViewAccessibility::SetPopupFocusOverride() {}
 
 void ViewAccessibility::EndPopupFocusOverride() {}
 
-bool ViewAccessibility::IsFocusedForTesting() {
+bool ViewAccessibility::IsFocusedForTesting() const {
   return view_->HasFocus() && !focused_virtual_child_;
 }
 
@@ -329,11 +329,11 @@ void ViewAccessibility::OverridePreviousFocus(Widget* widget) {
   previous_focus_ = widget;
 }
 
-Widget* ViewAccessibility::GetNextFocus() {
+Widget* ViewAccessibility::GetNextFocus() const {
   return next_focus_;
 }
 
-Widget* ViewAccessibility::GetPreviousFocus() {
+Widget* ViewAccessibility::GetPreviousFocus() const {
   return previous_focus_;
 }
 

ui/views/accessibility/view_accessibility.h

@@ -83,20 +83,23 @@ class VIEWS_EXPORT ViewAccessibility {
   void OverrideDescribedBy(View* described_by_view);
   void OverrideHasPopup(const ax::mojom::HasPopup has_popup);
 
-  // Override indexes used by some screen readers when describing elements in a
-  // menu, list, etc. If not specified, a view's index in its parent and its
-  // parent's number of children provide the values for these.
+  // Override information provided to users by screen readers when describing
+  // elements in a menu, listbox, or another set-like item. For example, "New
+  // tab, menu item 1 of 5". If not specified, a view's index in its parent and
+  // its parent's number of children provide the values for |pos_in_set| and
+  // |set_size| respectively.
   //
-  // Note: |pos_in_set| is 1-indexed.
+  // Note that |pos_in_set| is one-based, i.e. it starts from 1 not 0.
   void OverridePosInSet(int pos_in_set, int set_size);
 
-  // Override the next or previous focused widget. Some screen readers may
-  // utilize this information to transition focus from the beginning or end of
-  // one window to another when navigating by its default navigation method.
+  // Override the next or previous focused widget. Some assistive technologies,
+  // such as screen readers, may utilize this information to transition focus
+  // from the beginning or end of one widget to another when navigating by its
+  // default navigation method.
   void OverrideNextFocus(Widget* widget);
   void OverridePreviousFocus(Widget* widget);
-  Widget* GetNextFocus();
-  Widget* GetPreviousFocus();
+  Widget* GetNextFocus() const;
+  Widget* GetPreviousFocus() const;
 
   // Returns the accessibility object that represents the View whose
   // accessibility is managed by this instance. This may be an AXPlatformNode or
@@ -164,7 +167,7 @@ class VIEWS_EXPORT ViewAccessibility {
   virtual void EndPopupFocusOverride();
 
   // Return true if this view is considered focused.
-  virtual bool IsFocusedForTesting();
+  virtual bool IsFocusedForTesting() const;
 
   // Call when a menu closes, to restore focus to where it was previously.
   virtual void FireFocusAfterMenuClose();
@@ -212,6 +215,8 @@ class VIEWS_EXPORT ViewAccessibility {
   // "presentational".
   bool is_ignored_;
 
+  // Used by the Views system to help some assistive technologies, such as
+  // screen readers, transition focus from one widget to another.
   Widget* next_focus_ = nullptr;
   Widget* previous_focus_ = nullptr;
 };

ui/views/accessibility/view_ax_platform_node_delegate.cc

@@ -159,7 +159,7 @@ void ViewAXPlatformNodeDelegate::EndPopupFocusOverride() {
   ui::AXPlatformNode::SetPopupFocusOverride(nullptr);
 }
 
-bool ViewAXPlatformNodeDelegate::IsFocusedForTesting() {
+bool ViewAXPlatformNodeDelegate::IsFocusedForTesting() const {
   if (ui::AXPlatformNode::GetPopupFocusOverride())
     return ui::AXPlatformNode::GetPopupFocusOverride() ==
            GetNativeViewAccessible();

ui/views/accessibility/view_ax_platform_node_delegate.h

@@ -96,7 +96,7 @@ class ViewAXPlatformNodeDelegate : public ViewAccessibility,
   base::Optional<int> GetSetSize() const override;
   void SetPopupFocusOverride() override;
   void EndPopupFocusOverride() override;
-  bool IsFocusedForTesting() override;
+  bool IsFocusedForTesting() const override;
 
  protected:
   explicit ViewAXPlatformNodeDelegate(View* view);