[wasm] Cleanup %IsAsmWasmCode testing predicate.

test/mjsunit/asm/asm-validation.js

Index: test/mjsunit/asm/asm-validation.js
diff --git a/test/mjsunit/asm/asm-validation.js b/test/mjsunit/asm/asm-validation.js
index d4c6fff1cf76f5c8cbaf8cbb374fb3dba92168a5..a7935dc2c1770700b37bff39b718d11282813f77 100644
--- a/test/mjsunit/asm/asm-validation.js
+++ b/test/mjsunit/asm/asm-validation.js
@@ -4,6 +4,12 @@
 
 // Flags: --validate-asm --allow-natives-syntax
 
+// Note that this test file contains tests that explicitly check modules are
+// valid asm.js and then break them with invalid instantiation arguments. If
+// this script is run more than once (e.g. --stress-opt) then modules remain
+// broken in the second run and assertions would fail. We prevent re-runs.
+// Flags: --nostress-opt
+
 function assertValidAsm(func) {
   assertTrue(%IsAsmWasmCode(func));
 }