Merge to XFA: Add missing operators for CFX_xxxString combo patch.

This pulls in:
Review URL: https://codereview.chromium.org/1099193002
Review URL: https://codereview.chromium.org/1090303003
Review URL: https://codereview.chromium.org/1084293003
Review URL: https://codereview.chromium.org/1099213002

Plus one fix to an XFA file to fix compilation.

TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1095893005