Remove repeated "success" check from compileTreeImpl This refactoring simplifies the compilation code by putting AST checks and simplification into a separate function. This function will immediately return false when an error is encountered. This is easier to maintain than repeated checking of a "success" boolean. BUG=angleproject:2068 TEST=WebGL conformance tests, angle_unittests, angle_end2end_tests Change-Id: I1ae1c8def3625ada1482104a6babe605405229ef Reviewed-on: https://chromium-review.googlesource.com/750085 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>