Move MdFocusRing to be a property of FocusManager.

ui/views/focus/focus_manager.cc

Index: ui/views/focus/focus_manager.cc
diff --git a/ui/views/focus/focus_manager.cc b/ui/views/focus/focus_manager.cc
index 80a4dc8d6bdd0c7b67ee984e6081e434cebe6db1..7d43a449cbd568999cb26d7971ddb7d5b955b251 100644
--- a/ui/views/focus/focus_manager.cc
+++ b/ui/views/focus/focus_manager.cc
@@ -15,6 +15,8 @@
 #include "ui/base/ime/text_input_client.h"
 #include "ui/events/event.h"
 #include "ui/events/keycodes/keyboard_codes.h"
+#include "ui/gfx/canvas.h"
+#include "ui/native_theme/native_theme.h"
 #include "ui/views/focus/focus_manager_delegate.h"
 #include "ui/views/focus/focus_search.h"
 #include "ui/views/focus/view_storage.h"
@@ -26,6 +28,71 @@
 
 namespace views {
 
+namespace internal {
+
+// The stroke width of the focus border in dp.
+const int kFocusBorderThickness = 2;
+
+// The corner radius of the focus border roundrect.
+const int kFocusBorderCornerRadius = 3;
+
+// MdFocusRing is a View that is parented to the currently focused View.
+// It paints a ring around the view to indicate focus, and extends slightly
+// beyond the bounds of the view. By having a single focus ring per
+// FocusManager, we reduce the number of views and layers as well as the
+// number of focus change observers.
+class MdFocusRing : public View {
+ public:
+  MdFocusRing() {
+    // A layer is necessary to paint beyond the parent's bounds.
+    SetPaintToLayer(true);
+    layer()->SetFillsBoundsOpaquely(false);
+    set_owned_by_client();
+  }
+  ~MdFocusRing() override {}
+
+  void Install(views::View* focused_view) {
+    focused_view->AddChildView(this);
+    Layout();
+  }
+
+  void Uninstall(views::View* unfocused_view) {
+    if (parent() != unfocused_view)
+      return;
+    parent()->RemoveChildView(this);
+  }
+
+  // View:
+  bool CanProcessEventsWithinSubtree() const override { return false; }
+
+  void Layout() override {
+    // The focus ring handles its own sizing, which is simply to fill the parent
+    // and extend a little beyond its borders.
+    gfx::Rect focus_bounds = parent()->GetLocalBounds();
+    focus_bounds.Inset(gfx::Insets(-kFocusBorderThickness));
+    SetBoundsRect(focus_bounds);
+  }
+
+  void OnPaint(gfx::Canvas* canvas) override {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setColor(
+        SkColorSetA(GetNativeTheme()->GetSystemColor(
+                        ui::NativeTheme::kColorId_FocusedBorderColor),
+                    0x66));
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setStrokeWidth(kFocusBorderThickness);
+    gfx::RectF rect(GetLocalBounds());
+    rect.Inset(gfx::InsetsF(kFocusBorderThickness / 2.f));
+    canvas->DrawRoundRect(rect, kFocusBorderCornerRadius, paint);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MdFocusRing);
+};
+
+}  // namespace internal
+
 bool FocusManager::arrow_key_traversal_enabled_ = false;
 
 FocusManager::FocusManager(Widget* widget, FocusManagerDelegate* delegate)
@@ -36,7 +103,8 @@ FocusManager::FocusManager(Widget* widget, FocusManagerDelegate* delegate)
       shortcut_handling_suspended_(false),
       focus_change_reason_(kReasonDirectFocusChange),
       is_changing_focus_(false),
-      keyboard_accessible_(false) {
+      keyboard_accessible_(false),
+      focus_ring_(nullptr) {
   DCHECK(widget_);
   stored_focused_view_storage_id_ =
       ViewStorage::GetInstance()->CreateStorageID();
@@ -322,14 +390,23 @@ void FocusManager::SetFocusedViewWithReason(
 
   View* old_focused_view = focused_view_;
   focused_view_ = view;
-  if (old_focused_view)
+  if (old_focused_view) {
     old_focused_view->Blur();
+    if (focus_ring_)
+      focus_ring_->Uninstall(old_focused_view);
+  }
   // Also make |focused_view_| the stored focus view. This way the stored focus
   // view is remembered if focus changes are requested prior to a show or while
   // hidden.
   SetStoredFocusView(focused_view_);
-  if (focused_view_)
+  if (focused_view_) {
     focused_view_->Focus();
+    if (focused_view_->should_use_md_focus_ring()) {
+      if (!focus_ring_)
+        focus_ring_.reset(new internal::MdFocusRing());
+      focus_ring_->Install(focused_view_);
+    }
+  }
 
   FOR_EACH_OBSERVER(FocusChangeListener, focus_change_listeners_,
                     OnDidChangeFocus(old_focused_view, focused_view_));