Add a policy to disable mounting of external storage.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 9953cfd777a660d71402ca9e6fc791dff1b0b9dd..a44dcb475944ab63e6f5625ec2d3fd380434bd09 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1778,6 +1778,10 @@ const char kDeviceLocation[] = "device_status.location";
 // A string that is used to store first-time sync startup after once sync is
 // disabled. This will be refreshed every sign-in.
 const char kSyncSpareBootstrapToken[] = "sync.spare_bootstrap_token";
+
+// A pref holding the value of the policy used to disable mounting of external
+// storage for the user.
+const char kExternalStorageDisabled[] = "hardware.external_storage_disabled";
 #endif
 
 // Whether there is a Flash version installed that supports clearing LSO data.