tree ce64b9a0f76ead39b10169d50bfdb1169d5dcbcc
parent 4dcb83a0ae8ced6b200876d90f90b185e379089e
author Todd Wang <toddw@google.com> 1456782555 -0800
committer Todd Wang <toddw@google.com> 1456782555 -0800

lib: Add helper functions to envvar to manipulate token lists.

Renames {Prepend,Append}UsingSeparator to
{Prepend,Append}UniqueToken, and changes the semantics to also
filter away duplicate tokens.  The previous functions didn't seem
to provide much value over manually calling {Split,Join}Tokens.
The new functions provide a bit more functionalty wrapped into a
one-line call.

Also added UniqueTokens and FilterTokens, which help manipulate
slices of tokens.

MultiPart: 2/2

Change-Id: Ice2c126615af17ff43804c472826d738e5724608