"platforms" in privacy.json should be "chromeos" not "cros".

chrome/common/extensions/api/privacy.json

Index: chrome/common/extensions/api/privacy.json
diff --git a/chrome/common/extensions/api/privacy.json b/chrome/common/extensions/api/privacy.json
index a74b5056ff9a3282c2ee0daa4831f324455d0db7..d1068c6b75f0ceec7ccf0d30a24d9857bd6918e3 100644
--- a/chrome/common/extensions/api/privacy.json
+++ b/chrome/common/extensions/api/privacy.json
@@ -85,7 +85,7 @@
             "$ref": "types.ChromeSetting",
             "value": ["protectedContentEnabled", {"type":"boolean"}],
             "description": "<strong>Available on ChromeOS only</strong>: If enabled, Chrome provides a unique ID to plugins in order to run protected content. The value of this preference is of type boolean, and the default value is <code>true</code>.",
-            "platforms": ["cros", "cros touch"]
+            "platforms": ["chromeos", "chromeos touch"]
           }
         }
       }