[iOS CBCM] Add explanation about machine name on iOS

Adds a comment explaining the decision to use Apple's device identifier
rather than the user-entered device name for cloud reporting. The goal
is to prevent accidentally switching to the user device name in the
future.

Bug: 1123949
Change-Id: If03a6531662297a2598d970822ef04ecb4666787
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2388600Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Guillaume Jenkins <gujen@google.com>
Cr-Commit-Position: refs/heads/master@{#803620}

components/policy/core/common/cloud/cloud_policy_util.cc

@@ -83,6 +83,9 @@ std::string GetMachineName() {
 #elif defined(OS_APPLE)
 
 #if defined(OS_IOS)
+  // The user-entered device name (e.g. "Foo's iPhone") should not be used, as
+  // there are privacy considerations (crbug.com/1123949). The Apple internal
+  // device name (e.g. "iPad6,11") is used instead.
   std::string ios_model_name = base::SysInfo::HardwareModelName();
   if (!ios_model_name.empty()) {
     return ios_model_name;