MacViews: Implement Full Keyboard Access.

ui/views/view.h

Index: ui/views/view.h
diff --git a/ui/views/view.h b/ui/views/view.h
index 897160ea199e36d922f15edd57ae0e1e646e3653..7376fc81be06419f9a90f8b269f50d1210913952 100644
--- a/ui/views/view.h
+++ b/ui/views/view.h
@@ -115,6 +115,22 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
  public:
   typedef std::vector<View*> Views;
 
+  enum class FocusBehavior {
+    // Use when the view is to be focusable both in default and full keyboard
+    // access mode.
+    ALWAYS,
+
+    // Use when view is never focusable. Default.
+    NEVER,
+
+    // Use when the view is to be made focusable only during full keyboard mode.
+    ACCESSIBLE_ONLY,
+
+    // Use for controls. On Mac, this is the same as ACCESSIBLE_ONLY mode, while
+    // on other platforms it corresponds to ALWAYS.
+    CONTROL,

[sky, 2016/04/12 16:39:52]

CONTROL sounds good, but in practice it is really CONTROL_AS_UNDERSTOOD_BY_OSX,
which is hardly satisfying. The table approach I outlined and you implemented
here https://codereview.chromium.org/1870573003 suffers from needing a
centralized list of all possible controls. I'm ok with that approach, but the
ui/views code shouldn't contain a list of leaf view nodes defined else where,
e.g. DESKTOP_MEDIA_SOURCE_VIEW should be in chrome. That means you need both a
platformstyle in ui/views and one in other places defined their own leaf view
nodes (such as chrome, but likely other places as well).

I'm leaning toward ifdefs in the controls themselves. This avoids needing
multiple lists, and it avoids CONTROL_AS_UNDERSTOOD_BY_OSX.

More concretely I'm saying keep the FocusBehavior you have here, but not
CONTROL. Code like that in button becomes:

namespace {
View::FocusBehavior GetButtonFocusBehavior() {
#if defined(OS_MACOSX)
  return FocusBehavior::ACCESSIBLE_ONLY;
#else
  return FocusBehavior::ALWAYS;
#endif
}
}  // namespace

SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);

Thoughts?

+  };
+
   struct ViewHierarchyChangedDetails {
     ViewHierarchyChangedDetails()
         : is_add(false),
@@ -768,10 +784,15 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   // IMPORTANT NOTE: loops in the focus hierarchy are not supported.
   void SetNextFocusableView(View* view);
 
+  // Sets |focusable_| and |accessibility_focusable_| corresponding to the given
+  // |focus_behavior|.
+  void SetFocusBehavior(FocusBehavior focus_behavior);
+
   // Sets whether this view is capable of taking focus. It will clear focus if
   // the focused view is set to be non-focusable.
   // Note that this is false by default so that a view used as a container does
   // not get the focus.
+  // TODO(karandeepb): Make private.
   void SetFocusable(bool focusable);
 
   // Returns true if this view is |focusable_|, |enabled_| and drawn.
@@ -785,6 +806,7 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   // full keyboard access, even though it's not normally focusable. It will
   // clear focus if the focused view is set to be non-focusable.
   // Note that this is false by default.
+  // TODO(karandeepb): Make private.
   void SetAccessibilityFocusable(bool accessibility_focusable);
 
   // Convenience method to retrieve the FocusManager associated with the