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..86d58502c9c205dd3255fcf8e50a21266b40711b 100644
--- a/base/sys_info_mac.mm
+++ b/base/sys_info_mac.mm
@@ -96,16 +96,23 @@ int64_t SysInfo::AmountOfAvailablePhysicalMemory() {
 std::string SysInfo::CPUModelName() {
   char name[256];
   size_t len = arraysize(name);
-  if (sysctlbyname("machdep.cpu.brand_string", &name, &len, NULL, 0) == 0)
-    return name;
+  if (sysctlbyname("machdep.cpu.brand_string", &name, &len, nullptr, 0) == 0) {
+    DCHECK_GE(len, 1u);
+    DCHECK_EQ('\0', name[len - 1]);
+    return std::string(name, len - 1);
+  }
   return std::string();
 }
 
+// static
 std::string SysInfo::HardwareModelName() {
   char model[256];
   size_t len = sizeof(model);
-  if (sysctlbyname("hw.model", model, &len, NULL, 0) == 0)
-    return std::string(model, 0, len);
+  if (sysctlbyname("hw.model", model, &len, nullptr, 0) == 0) {
+    DCHECK_GE(len, 1u);
+    DCHECK_EQ('\0', model[len - 1]);
+    return std::string(model, len - 1);
+  }
   return std::string();
 }