Implement RemovableDeviceNotifications for Mac

base/sys_string_conversions_mac.mm

Index: base/sys_string_conversions_mac.mm
diff --git a/base/sys_string_conversions_mac.mm b/base/sys_string_conversions_mac.mm
index d1e37432f92eac06cdd9e1fb224006313ef4573a..97c796974e65ddf5ab1834c6b28b9b150ffe249a 100644
--- a/base/sys_string_conversions_mac.mm
+++ b/base/sys_string_conversions_mac.mm
@@ -163,11 +163,15 @@ NSString* SysUTF16ToNSString(const string16& utf16) {
 }
 
 std::string SysCFStringRefToUTF8(CFStringRef ref) {
+  if (!ref)
+    return std::string();
   return CFStringToSTLStringWithEncodingT<std::string>(ref,
                                                        kNarrowStringEncoding);
 }
 
 string16 SysCFStringRefToUTF16(CFStringRef ref) {
+  if (!ref)
+    return string16();
   return CFStringToSTLStringWithEncodingT<string16>(ref,
                                                     kMediumStringEncoding);
 }