Animate the accessibility focus ring and fix some minor visual issues.

chrome/browser/chromeos/ui/accessibility_focus_ring.h

Index: chrome/browser/chromeos/ui/accessibility_focus_ring.h
diff --git a/chrome/browser/chromeos/ui/accessibility_focus_ring.h b/chrome/browser/chromeos/ui/accessibility_focus_ring.h
index 3185d31e3ff1fb9b9d6a21b901fe3aa57efea7c1..0cce26194a34c030b1f41217b1ee0d715e21887a 100644
--- a/chrome/browser/chromeos/ui/accessibility_focus_ring.h
+++ b/chrome/browser/chromeos/ui/accessibility_focus_ring.h
@@ -72,6 +72,13 @@ struct AccessibilityFocusRing {
   static AccessibilityFocusRing CreateWithRect(
       const gfx::Rect& bounds, int margin);
 
+  // Returns a ring where 0.0 returns r1, 1.0 returns r2, and any number
+  // in-between interpolates linearly between them.
+  static AccessibilityFocusRing Interpolate(
+      const AccessibilityFocusRing& r1,
+      const AccessibilityFocusRing& r2,
+      double fraction);
+
   // Construct an AccessibilityFocusRing that outlines a paragraph-shaped
   // object.
   static AccessibilityFocusRing CreateWithParagraphShape(