Increase visibility of a11y dashed focus ring

Currently, when a secondary color is used with a dashed focus ring,
it is hard to see, because its width is split across both sides of the
primary color. This change increases the width on either side to
increase visibility.

AX-Relnotes: n/a.
Bug: 1094069
Change-Id: If68505b4f374c3e0af0f09c8c7649d819edc7126
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2244192Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/master@{#778907}

ash/accessibility/accessibility_focus_ring_layer.cc

@@ -178,7 +178,7 @@ void AccessibilityFocusRingLayer::DrawDashedFocusRing(
   // To keep the dashes properly lined up, we will draw the outside line first,
   // and cover it with the inner line.
   flags.setColor(secondary_color_);
-  flags.setStrokeWidth(2 * kDefaultStrokeWidth);
+  flags.setStrokeWidth(3 * kDefaultStrokeWidth);
 
   path = MakePath(ring_, 0, offset);
   recorder.canvas()->DrawPath(path, flags);