Change access mode of disk devices when mounting based on config.

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 a39495ef32ebc45c8380be429356c7f907e733fb..8e8c54276e541643635fc3cf4b660a58b4128916 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1734,6 +1734,10 @@ const char kDeviceLocation[] = "device_status.location";
 // storage for the user.
 const char kExternalStorageDisabled[] = "hardware.external_storage_disabled";
 
+// A pref holding the value of the policy used to limit mounting of external
+// storage to read-only mode for the user.
+const char kExternalStorageReadOnly[] = "hardware.external_storage_read_only";
+
 // Copy of owner swap mouse buttons option to use on login screen.
 const char kOwnerPrimaryMouseButtonRight[] = "owner.mouse.primary_right";