Prepend starboard OS name in user-agent string

The current OS name in user-agent string is fetched using
chromium code which just return "Linux". This misses the real
OS name for starboard platform and result in YTS test failure.
So OS name in user-agent string should include the starboard platform
OS name.

Bug: 475670748

Author: Santosh Mahto

cobalt/browser/user_agent/user_agent_platform_info.cc

@@ -190,7 +190,9 @@ void UserAgentPlatformInfo::InitializePlatformDependentFieldsAndroid() {
 }
 #elif BUILDFLAG(IS_STARBOARD)
 void UserAgentPlatformInfo::InitializePlatformDependentFieldsStarboard() {
-  const std::string os_name = base::SysInfo::OperatingSystemName();
+  std::string os_name =
+      starboard::GetSystemPropertyString(kSbSystemPropertyFriendlyName) + "; " +
+      base::SysInfo::OperatingSystemName();
   const std::string os_version = base::SysInfo::OperatingSystemVersion();
   set_os_name_and_version(
       base::StringPrintf("%s %s", os_name.c_str(), os_version.c_str()));