Revert "Make CFX_WideString::LockBuffer() completely unused."

This reverts commit 5a256ad29483eb2b13e6e2c89fe0f77a9103f68f.
Reason for revert: broke JS tests.

TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1112673002
4 files changed