Handle interface blocks in getVariableInfo and getUserDefinedVariableInfo. BUG=angle:654 Change-Id: I07a230bbf2387e85168c50cb3719c669a7890f8a Reviewed-on: https://chromium-review.googlesource.com/199687 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Shannon Woods <shannonwoods@chromium.org>