HID report descriptors not available before OS X 10.8.

On OS X Snow Leopard and Lion (currently supported by Chrome) the
kIOHIDReportDescriptorKey is not available as it is in later versions of
the operating system. Since we are also unable to get the device's
report descriptor on Windows it seems okay to just ignore the failure.

BUG=479210

Review URL: https://codereview.chromium.org/1373923003

Cr-Commit-Position: refs/heads/master@{#351183}

device/hid/hid_service_mac.cc

@@ -254,8 +254,7 @@ scoped_refptr<HidDeviceInfo> HidServiceMac::CreateDeviceInfo(
   std::vector<uint8> report_descriptor;
   if (!TryGetHidDataProperty(hid_device, CFSTR(kIOHIDReportDescriptorKey),
                              &report_descriptor)) {
-    HID_LOG(EVENT) << "Unable to get report descriptor for new device.";
-    return nullptr;
+    HID_LOG(DEBUG) << "Device report descriptor not available.";
   }
 
   return new HidDeviceInfo(