[no-wasm] Make --expose-wasm flag readonly

If webassembly is disabled via a gn arg, we will not be able to enable
it via command-line switch. Hence make this flag read-only in that
configuration.

R=ecmziegler@chromium.org

Bug: v8:11238
Change-Id: Ib93a55f74d4f018477f110b8b52aa9b645e86553
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2710426Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Emanuel Ziegler <ecmziegler@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72905}

src/flags/flag-definitions.h

@@ -829,7 +829,7 @@ DEFINE_BOOL(wasm_generic_wrapper, true,
 #ifdef V8_ENABLE_WEBASSEMBLY
 DEFINE_BOOL(expose_wasm, true, "expose wasm interface to JavaScript")
 #else
-DEFINE_BOOL(expose_wasm, false, "expose wasm interface to JavaScript")
+DEFINE_BOOL_READONLY(expose_wasm, false, "expose wasm interface to JavaScript")
 #endif
 DEFINE_INT(wasm_num_compilation_tasks, 128,
            "maximum number of parallel compilation tasks for wasm")

src/init/v8.cc

@@ -119,7 +119,11 @@ void V8::InitializeOncePerProcessImpl() {
   // TODO(jgruber): Remove this once / if wasm can run without executable
   // memory.
   if (FLAG_jitless && !FLAG_correctness_fuzzer_suppressions) {
+#if V8_ENABLE_WEBASSEMBLY
     FLAG_expose_wasm = false;
+#else
+    STATIC_ASSERT(!FLAG_expose_wasm);
+#endif
   }
 
   if (FLAG_regexp_interpret_all && FLAG_regexp_tier_up) {

test/unittests/objects/value-serializer-unittest.cc

@@ -2480,6 +2480,7 @@ TEST_F(ValueSerializerTestWithHostArrayBufferView, RoundTripUint8ArrayInput) {
   ExpectScriptTrue("result.a === result.b");
 }
 
+#if V8_ENABLE_WEBASSEMBLY
 // It's expected that WebAssembly has more exhaustive tests elsewhere; this
 // mostly checks that the logic to embed it in structured clone serialization
 // works correctly.
@@ -2731,6 +2732,7 @@ TEST_F(ValueSerializerTestWithWasm, ComplexObjectWithManyTransfer) {
   VerifyComplexObject(value);
   ExpectScriptTrue("result.mod1 != result.mod2");
 }
+#endif  // V8_ENABLE_WEBASSEMBLY
 
 class ValueSerializerTestWithLimitedMemory : public ValueSerializerTest {
  protected: