It is apparently confusing that the `synchronized` parameter exists in
the class signature of each resource subclass, but it's not documented
anywhere. This change moves the parameter to _synchronized and pushes
documentation of the parameter down to the new/existing methods, as it's
not directly useful to end-users in the initializer, but is necessary in
those classmethods.
Change-Id: I42a01f24d44383889cccce2a2e89442eea1943d7
Closes-Bug: 1645007
2be9e9b6ba