Try to fix a crash in the new sync machine code

sync/util/get_session_name_mac.mm

Index: sync/util/get_session_name_mac.mm
diff --git a/sync/util/get_session_name_mac.mm b/sync/util/get_session_name_mac.mm
index b8eb25e3e94d12f3842699e11211c793f2d7c22c..7f5940b5a040d9c7cf63cb58df5ff58d377719a4 100644
--- a/sync/util/get_session_name_mac.mm
+++ b/sync/util/get_session_name_mac.mm
@@ -5,8 +5,10 @@
 #include "sync/util/get_session_name_mac.h"
 
 #import <SystemConfiguration/SCDynamicStoreCopySpecific.h>
+#include <sys/sysctl.h>
 
 #include "base/mac/scoped_cftyperef.h"
+#include "base/string_util.h"
 #include "base/sys_string_conversions.h"
 
 namespace syncer {
@@ -16,10 +18,31 @@ std::string GetHardwareModelName() {
   // Do not use NSHost currentHost, as it's very slow. http://crbug.com/138570
   SCDynamicStoreContext context = { 0, NULL, NULL, NULL };
   base::mac::ScopedCFTypeRef<SCDynamicStoreRef> store(
-      SCDynamicStoreCreate(kCFAllocatorDefault, CFSTR("policy_subsystem"),
+      SCDynamicStoreCreate(kCFAllocatorDefault, CFSTR("chrome_sync"),
                            NULL, &context));
-  CFStringRef machine_name = SCDynamicStoreCopyLocalHostName(store.get());
-  return base::SysCFStringRefToUTF8(machine_name);
+  base::mac::ScopedCFTypeRef<CFStringRef> machine_name(
+      SCDynamicStoreCopyLocalHostName(store.get()));
+  if (machine_name.get())
+    return base::SysCFStringRefToUTF8(machine_name.get());
+
+  // Fall back to get computer name.
+  base::mac::ScopedCFTypeRef<CFStringRef> computer_name(
+      SCDynamicStoreCopyComputerName(store.get(), NULL));
+  if (computer_name.get())
+    return base::SysCFStringRefToUTF8(computer_name.get());
+
+  // If all else fails, return to using a slightly nicer version of the
+  // hardware model.
+  char modelBuffer[256];
+  size_t length = sizeof(modelBuffer);
+  if (!sysctlbyname("hw.model", modelBuffer, &length, NULL, 0)) {
+    for (size_t i = 0; i < length; i++) {
+      if (IsAsciiDigit(modelBuffer[i]))
+        return std::string(modelBuffer, 0, i);
+    }
+    return std::string(modelBuffer, 0, length);
+  }
+  return "Unknown";
 }
 
 }  // namespace internal