[wasm] enable wasm structured cloning in specific cases

third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp

Index: third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp b/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
index 267a8ab5d524f53eef7a08b165e1bb09ee43be50..04bb0863400f593c813b542254479918bc0a3976 100644
--- a/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/serialization/V8ScriptValueSerializer.cpp
@@ -49,7 +49,8 @@ V8ScriptValueSerializer::V8ScriptValueSerializer(
       m_serializedScriptValue(SerializedScriptValue::create()),
       m_serializer(m_scriptState->isolate(), this),
       m_transferables(options.transferables),
-      m_blobInfoArray(options.blobInfo) {}
+      m_blobInfoArray(options.blobInfo),
+      m_inlineWasm(options.writeWasmToStream) {}
 
 RefPtr<SerializedScriptValue> V8ScriptValueSerializer::serialize(
     v8::Local<v8::Value> value,
@@ -420,6 +421,22 @@ v8::Maybe<uint32_t> V8ScriptValueSerializer::GetSharedArrayBufferId(
   return v8::Just<uint32_t>(index);
 }
 
+v8::Maybe<uint32_t> V8ScriptValueSerializer::GetWasmModuleTransferId(
+    v8::Isolate* isolate,
+    v8::Local<v8::WasmCompiledModule> module) {
+  if (m_inlineWasm)
+    return v8::Nothing<uint32_t>();

[jbroman, 2017/03/27 18:50:52]

nit: The usual expectation is that functions returning Maybe across the API
boundary throw an exception when they return nothing.

Also, should we NOTREACHED() in this case? Should v8 ever be calling this in the
case where we are writing wasm inline?

[Mircea Trofin, 2017/03/27 20:52:33]

See prev comment re. exceptions.

On the serialization side, v8 will try first to transfer, and if the delegate
provides Nothing<bool>, then it goes the inline path. So we can't NOTREACHED()
here.

[jbroman, 2017/03/28 15:27:25]

OK. Please add this to the documentation in include/v8.h (actually, I don't
think there's a comment there at all right now), because this is surprising
behaviour to me.

+  // We don't expect scenarios with numerous wasm modules being transferred
+  // around. Most likely, we'll have one module. The vector approach is simple
+  // and should perform sufficiently well under these expectations.
+  this->m_serializedScriptValue->wasmModules().push_back(
+      module->GetTransferrableModule());
+  uint32_t size =
+      static_cast<uint32_t>(m_serializedScriptValue->wasmModules().size());
+  DCHECK_GE(size, 1u);
+  return v8::Just(size - 1);
+}
+
 void* V8ScriptValueSerializer::ReallocateBufferMemory(void* oldBuffer,
                                                       size_t size,
                                                       size_t* actualSize) {