Track whether a name is internal to ANGLE in a separate class The AST contains identifiers in a few different places: besides symbols, there are also function names, which show up in function signatures and function calls. Any of these can be coming either from the original shader or from inside ANGLE. A class that encapsulates a string and its internalness will be useful for implementing a unified way of handling all names in shader translation. Start implementing this by splitting the functionality out of TSymbol. TEST=angle_unittests BUG=angleproject:1116 Change-Id: I0a1b5936dcccd0d5fc1c0c13c712102fbfff2a79 Reviewed-on: https://chromium-review.googlesource.com/291280 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com>