Cros: Add focus ring to shelf app button

As we moved from mask layers to highlight paths for ink drops, we
removed the focus ring.
This change re-enables it.

Bug: 1046176
Change-Id: I028fdee9543fac3710243f45227d4f88921425f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2119638Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Ana Salazar <anasalazar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753655}

ash/shelf/shelf_app_button.cc

@@ -38,6 +38,7 @@
 #include "ui/views/controls/highlight_path_generator.h"
 #include "ui/views/controls/image_view.h"
 #include "ui/views/painter.h"
+#include "ui/views/style/platform_style.h"
 
 namespace {
 
@@ -336,6 +337,14 @@ ShelfAppButton::ShelfAppButton(ShelfView* shelf_view,
 
   // Do not set a clip, allow the ink drop to burst out.
   views::InstallEmptyHighlightPathGenerator(this);
+  SetFocusBehavior(FocusBehavior::ALWAYS);
+  SetInstallFocusRingOnFocus(true);
+  focus_ring()->SetColor(ShelfConfig::Get()->shelf_focus_border_color());
+  // The focus ring should have an inset of half the focus border thickness, so
+  // the parent view won't clip it.
+  focus_ring()->SetPathGenerator(
+      std::make_unique<views::RoundRectHighlightPathGenerator>(
+          gfx::Insets(views::PlatformStyle::kFocusHaloThickness / 2, 0), 0));
 }
 
 ShelfAppButton::~ShelfAppButton() {
@@ -699,6 +708,7 @@ void ShelfAppButton::Layout() {
   indicator_->SetBoundsRect(indicator_bounds);
 
   UpdateState();
+  focus_ring()->Layout();
 }
 
 void ShelfAppButton::ChildPreferredSizeChanged(views::View* child) {