Implement SysInfo::HardwareModelName() on iOS.

base/sys_info_mac.mm

Index: base/sys_info_mac.mm
diff --git a/base/sys_info_mac.mm b/base/sys_info_mac.mm
index 1141bd557768bab8eb387dd62668831edd40bd92..63513f7b1f0033c79623c302d01ac51fe1217d44 100644
--- a/base/sys_info_mac.mm
+++ b/base/sys_info_mac.mm
@@ -101,6 +101,7 @@ std::string SysInfo::CPUModelName() {
   return std::string();
 }
 
+// static
 std::string SysInfo::HardwareModelName() {
   char model[256];
   size_t len = sizeof(model);