Fix focus ring for downloads section header.

Though the entire downloads section header is focusable and behaves as
a single button, the focus ring is drawn as a circle around just the
chevron.

Screenshot: http://shortn/_yNqR9nC2Pk

Bug: 1160011
Change-Id: Ie58083966e5bf1d01b09472cc7271b978741b91f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2628747
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843687}

ash/system/holding_space/downloads_section.cc

@@ -19,6 +19,7 @@
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/views/accessibility/view_accessibility.h"
 #include "ui/views/controls/button/button.h"
+#include "ui/views/controls/highlight_path_generator.h"
 #include "ui/views/controls/image_view.h"
 #include "ui/views/controls/label.h"
 #include "ui/views/layout/box_layout.h"
@@ -27,6 +28,26 @@ namespace ash {
 
 namespace {
 
+// CallbackPathGenerator -------------------------------------------------------
+
+class CallbackPathGenerator : public views::HighlightPathGenerator {
+ public:
+  using Callback = base::RepeatingCallback<gfx::RRectF()>;
+
+  explicit CallbackPathGenerator(Callback callback) : callback_(callback) {}
+  CallbackPathGenerator(const CallbackPathGenerator&) = delete;
+  CallbackPathGenerator& operator=(const CallbackPathGenerator&) = delete;
+  ~CallbackPathGenerator() override = default;
+
+ private:
+  // views::HighlightPathGenerator:
+  base::Optional<gfx::RRectF> GetRoundRect(const gfx::RectF& rect) override {
+    return callback_.Run();
+  }
+
+  Callback callback_;
+};
+
 // Header ----------------------------------------------------------------------
 
 class Header : public views::Button {
@@ -37,11 +58,6 @@ class Header : public views::Button {
     SetCallback(
         base::BindRepeating(&Header::OnPressed, base::Unretained(this)));
 
-    // Focus ring.
-    AshColorProvider* const ash_color_provider = AshColorProvider::Get();
-    focus_ring()->SetColor(ash_color_provider->GetControlsLayerColor(
-        AshColorProvider::ControlsLayerType::kFocusRingColor));
-
     auto* layout = SetLayoutManager(std::make_unique<views::BoxLayout>(
         views::BoxLayout::Orientation::kHorizontal, gfx::Insets(),
         kHoldingSpaceDownloadsHeaderSpacing));
@@ -54,12 +70,33 @@ class Header : public views::Button {
     layout->SetFlexForView(label, 1);
 
     // Chevron.
+    AshColorProvider* const ash_color_provider = AshColorProvider::Get();
     auto* chevron = AddChildView(std::make_unique<views::ImageView>());
     chevron->SetFlipCanvasOnPaintForRTLUI(true);
     chevron->SetImage(gfx::CreateVectorIcon(
         kChevronRightIcon, kHoldingSpaceDownloadsChevronIconSize,
         ash_color_provider->GetContentLayerColor(
             AshColorProvider::ContentLayerType::kIconColorPrimary)));
+
+    // Focus ring.
+    focus_ring()->SetColor(ash_color_provider->GetControlsLayerColor(
+        AshColorProvider::ControlsLayerType::kFocusRingColor));
+
+    // Though the entirety of the header is focusable and behaves as a single
+    // button, the focus ring is drawn as a circle around just the `chevron`.
+    focus_ring()->SetPathGenerator(
+        std::make_unique<CallbackPathGenerator>(base::BindRepeating(
+            [](const views::View* chevron) {
+              const float radius = chevron->width() / 2.f;
+              gfx::RRectF path(gfx::RectF(chevron->bounds()), radius);
+              if (base::i18n::IsRTL()) {
+                // Manually adjust for flipped canvas in RTL.
+                path.Offset(-chevron->parent()->width(), 0.f);
+                path.Scale(-1.f, 1.f);
+              }
+              return path;
+            },
+            base::Unretained(chevron))));
   }
 
  private: