[Mac] Redesign the avatar bubble UI

ui/native_theme/fallback_theme.cc

Index: ui/native_theme/fallback_theme.cc
diff --git a/ui/native_theme/fallback_theme.cc b/ui/native_theme/fallback_theme.cc
index ffb15fd6626fc3bde40384e07b53e22efb19ba7d..ab6fc27aaea54597d05bd4bb48b68f12886fa293 100644
--- a/ui/native_theme/fallback_theme.cc
+++ b/ui/native_theme/fallback_theme.cc
@@ -36,6 +36,8 @@ SkColor FallbackTheme::GetSystemColor(ColorId color_id) const {
   static const SkColor kButtonDisabledColor = SkColorSetRGB(0x99, 0x99, 0x99);
   static const SkColor kButtonHighlightColor = SkColorSetRGB(0, 0, 0);
   static const SkColor kButtonHoverColor = kButtonEnabledColor;
+  static const SkColor kButtonHoverBackgroundColor =
+      SkColorSetRGB(0xEA, 0xEA, 0xEA);
   // MenuItem:
   static const SkColor kEnabledMenuItemForegroundColor = kButtonEnabledColor;
   static const SkColor kDisabledMenuItemForegroundColor = kButtonDisabledColor;
@@ -135,6 +137,8 @@ SkColor FallbackTheme::GetSystemColor(ColorId color_id) const {
       return kButtonHighlightColor;
     case kColorId_ButtonHoverColor:
       return kButtonHoverColor;
+    case kColorId_ButtonHoverBackgroundColor:
+      return kButtonHoverBackgroundColor;
 
     // MenuItem
     case kColorId_EnabledMenuItemForegroundColor: