Implement SysInfo::HardwareModelName() on iOS.

base/sys_info.h

Index: base/sys_info.h
diff --git a/base/sys_info.h b/base/sys_info.h
index f4134ea93a02fa4f677335e8bc86a98ec88588c1..b507f1306235b8953a8cae47261608789bc7dc8e 100644
--- a/base/sys_info.h
+++ b/base/sys_info.h
@@ -69,8 +69,9 @@ class BASE_EXPORT SysInfo {
 
   // Returns a descriptive string for the current machine model or an empty
   // string if the machine model is unknown or an error occured.
-  // e.g. "MacPro1,1" on Mac, or "Nexus 5" on Android. Only implemented on OS X,
-  // Android, and Chrome OS. This returns an empty string on other platforms.
+  // e.g. "MacPro1,1" on Mac, "iPhone9,3" on iOS or "Nexus 5" on Android. Only
+  // implemented on OS X, iOS, Android, and Chrome OS. This returns an empty
+  // string on other platforms.
   static std::string HardwareModelName();
 
   // Returns the name of the host operating system.