Improve themed drawing of item separator on DL shelf in MD.

BUG=none

Review-Url: https://codereview.chromium.org/1993313004
Cr-Commit-Position: refs/heads/master@{#394934}
diff --git a/chrome/browser/themes/theme_service.cc b/chrome/browser/themes/theme_service.cc
index 092dab23..149e9ef 100644
--- a/chrome/browser/themes/theme_service.cc
+++ b/chrome/browser/themes/theme_service.cc
@@ -441,6 +441,11 @@
       separator_color_cache_[key] = separator_color;
       return separator_color;
     }
+    case ThemeProperties::COLOR_TOOLBAR_VERTICAL_SEPARATOR: {
+      return SkColorSetA(
+          GetColor(ThemeProperties::COLOR_TOOLBAR_BUTTON_ICON, incognito),
+          0x4D);
+    }
     case ThemeProperties::COLOR_BACKGROUND_TAB: {
       // The tints here serve a different purpose than TINT_BACKGROUND_TAB.
       // That tint is used to create background tab images for custom themes by