[Mac] Redesign the avatar bubble UI

ui/native_theme/common_theme.cc

Index: ui/native_theme/common_theme.cc
diff --git a/ui/native_theme/common_theme.cc b/ui/native_theme/common_theme.cc
index 0e6b76bcc02e093a4e47625e5097f7194142faaa..49d59c8e1ddfd5739f7456c28837a084c93ecad1 100644
--- a/ui/native_theme/common_theme.cc
+++ b/ui/native_theme/common_theme.cc
@@ -32,6 +32,8 @@ const SkColor kEnabledMenuItemForegroundColor = SK_ColorBLACK;
 const SkColor kDisabledMenuItemForegroundColor = SkColorSetRGB(161, 161, 146);
 const SkColor kHoverMenuItemBackgroundColor =
     SkColorSetARGB(204, 255, 255, 255);
+// Button:
+const SkColor kButtonHoverBackgroundColor = SkColorSetRGB(0xEA, 0xEA, 0xEA);
 
 }  // namespace
 
@@ -79,6 +81,10 @@ bool CommonThemeGetSystemColor(NativeTheme::ColorId color_id, SkColor* color) {
     case NativeTheme::kColorId_ButtonDisabledColor:
       *color = kDisabledMenuItemForegroundColor;
       break;
+    // Button
+    case NativeTheme::kColorId_ButtonHoverBackgroundColor:
+      *color = kButtonHoverBackgroundColor;
+      break;
     default:
       return false;
   }