Check multiplication validity in ParseContext This improves separation of responsibilities in the code: ParseContext should handle operand type validation, while TIntermBinary::promote should ideally only determine the type of the node based on the operation and operands. BUG=angleproject:952 TEST=angle_unittests Change-Id: I9a8d8ede21cdf35de631623a62194c0da5c604d2 Reviewed-on: https://chromium-review.googlesource.com/372622 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Corentin Wallez <cwallez@chromium.org>