Implement dynamic cast to TIntermBranch * on TIntermNode On the TIntermNode class there is no Derived *getAsDerived() for TIntermBranch. This is needed for the shader debugger to determine the node type. BUG=angleproject:1320 Change-Id: I9ce07017ccdb206c06c296b003b31eab6c65653c Reviewed-on: https://chromium-review.googlesource.com/328281 Tryjob-Request: Tibor Ouden, den <tibordenouden@gmail.com> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>