[Variations] Add a comment for the FEATURE_WITH_PARAMS_VALUE_TYPE

The macro does not work on Chrome OS.

Bug: 805766
Change-Id: I503f095b2fb80032102782cb3e4ce5cffe4a2795
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762308Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688633}

components/flags_ui/feature_entry.h

@@ -72,6 +72,8 @@ struct FeatureEntry {
     // passed from the server in a trial config). When set to Enabled, the
     // feature is overriden to be enabled and empty set of parameters is used
     // boiling down to the default behavior in the code.
+    // TODO(crbug.com/805766): The resulting chrome://flags entries will not work on Chrome OS
+    // devices (but will work in the CrOS-emulated build on Linux).
     FEATURE_WITH_PARAMS_VALUE,
 
     // Corresponds to a command line switch where the value is treatead as a