Refactor MdFocusRing to make it easier to reuse on other controls.

ui/views/controls/focus_ring.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/views/controls/focus_ring.h"
+
+#include "ui/gfx/canvas.h"
+#include "ui/native_theme/native_theme.h"
+#include "ui/views/controls/focusable_border.h"
+
+namespace views {
+
+namespace {
+
+// The stroke width of the focus border in dp.
+constexpr float kFocusHaloThicknessDp = 2.f;
+
+// The focus indicator should hug the normal border, when present (as in the
+// case of text buttons). Since it's drawn outside the parent view, we have to
+// increase the rounding slightly.
+constexpr float kFocusHaloCornerRadiusDp =
+    FocusableBorder::kCornerRadiusDp + kFocusHaloThicknessDp / 2.f;
+
+}  // namespace
+
+FocusRing::FocusRing() {

[sky, 2016/10/03 23:53:15]

WDYT of making this take the View to add to?

+  // A layer is necessary to paint beyond the parent's bounds.
+  SetPaintToLayer(true);
+  layer()->SetFillsBoundsOpaquely(false);
+}
+
+FocusRing::~FocusRing() {}
+
+bool FocusRing::CanProcessEventsWithinSubtree() const {
+  return false;
+}
+
+void FocusRing::Layout() {
+  // 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(-kFocusHaloThicknessDp));
+  SetBoundsRect(focus_bounds);
+}
+
+void FocusRing::OnPaint(gfx::Canvas* canvas) {
+  SkPaint paint;
+  paint.setAntiAlias(true);
+  paint.setColor(SkColorSetA(GetNativeTheme()->GetSystemColor(
+                                 ui::NativeTheme::kColorId_FocusedBorderColor),
+                             0x66));
+  paint.setStyle(SkPaint::kStroke_Style);
+  paint.setStrokeWidth(kFocusHaloThicknessDp);
+  gfx::RectF rect(GetLocalBounds());
+  rect.Inset(gfx::InsetsF(kFocusHaloThicknessDp / 2.f));
+  canvas->DrawRoundRect(rect, kFocusHaloCornerRadiusDp, paint);
+}
+
+}  // namespace views