V8 is switching the underlying validator used for --validate-asm (i.e. the feature enabled in Chrome via --enable-features=AsmJsToWebAssembly). This will change the content of some validation warnings and hence require a rebaseline of some layout tests. Note that only the textual content of the warnings changes, not where and when these warnings appear.
Related V8 tracking bug: issue v8:6127
Comment 1 by bugdroid1@chromium.org
, May 4 2017