[wasm] Fix cloned deserialization of JS-to-WASM wrappers.

This fixes a corner-case where deserialization of a module containing
multiple exported functions of the same signature forgot to properly
unprotect the code-space. Test coverage has been added.

R=clemensh@chromium.org
TEST=mjsunit/wasm/compiled-module-serialization
BUG=chromium:804767

Change-Id: I0082303db19bcc14c4de30f29d604665e281d79d
Reviewed-on: https://chromium-review.googlesource.com/880844Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50799}

src/wasm/wasm-serialization.cc

@@ -741,6 +741,10 @@ MaybeHandle<WasmCompiledModule> DeserializeNativeModule(
                                         compiled_module->GetNativeModule());
   if (!deserializer.Read(data)) return {};
 
+  // TODO(6792): Wrappers below might be cloned using {Factory::CopyCode}. This
+  // requires unlocking the code space here. This should be moved into the
+  // allocator eventually.
+  CodeSpaceMemoryModificationScope modification_scope(isolate->heap());
   CompileJsToWasmWrappers(isolate, compiled_module, isolate->counters());
   WasmCompiledModule::ReinitializeAfterDeserialization(isolate,
                                                        compiled_module);

test/mjsunit/wasm/compiled-module-serialization.js

@@ -98,6 +98,26 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertEquals(clone.constructor, compiled_module.constructor);
 })();
 
+(function SerializeWrappersWithSameSignature() {
+  let builder = new WasmModuleBuilder();
+  builder.addFunction("main", kSig_i_v)
+    .addBody([kExprI32Const, 42])
+    .exportFunc();
+  builder.addFunction("main_same_signature", kSig_i_v)
+    .addBody([kExprI32Const, 23])
+    .exportFunc();
+
+  var wire_bytes = builder.toBuffer();
+  var compiled_module = new WebAssembly.Module(wire_bytes);
+  var serialized = %SerializeWasmModule(compiled_module);
+  var clone = %DeserializeWasmModule(serialized, wire_bytes);
+
+  assertNotNull(clone);
+  assertFalse(clone == undefined);
+  assertFalse(clone == compiled_module);
+  assertEquals(clone.constructor, compiled_module.constructor);
+})();
+
 (function SerializeAfterInstantiation() {
   let builder = new WasmModuleBuilder();
   builder.addFunction("main", kSig_i_v)