Further AST traversals should not be run in case the expression
complexity check failed and set success=false. Otherwise traversal
can result in stack overflow.

BUG=chromium:780545
TEST=WebGL conformance tests

Change-Id: Icfde8c051038c691563e199a6d3a17b1e8e5ebf5
Reviewed-on: https://chromium-review.googlesource.com/750781
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>