refactor: fix modernize-return-braced-init-list warnings (#44838)

* refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

* refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

NB: using the braced-initializer list uncovered an error here:
the float returned by std::floor() can't be implicitly cast to
an int. This is solved by using base::ClampFloor<int>() instead.
std::floor()

shell/browser/electron_browser_main_parts.cc

@@ -163,7 +163,7 @@ std::u16string MediaStringProvider(media::MessageId id) {
       return u"Communications";
 #endif
     default:
-      return std::u16string();
+      return {};
   }
 }