Reland "Replace the wire serializer with a no-op impl on disconnect"

This is a reland of e757c012be

It changes a global noop serializer from a global static to a local
function static that's constructed on first use.

Original change's description:
> Replace the wire serializer with a no-op impl on disconnect
>
> Now that the command serialization knows to no-op if
> GetCmdSpace returns nullptr, when the wire is disconnected,
> we can replace it with a no-op serializer that always returns
> nullptr.
>
> Bug: chromium:951558
> Change-Id: I7363fd10f529119e515eda0e743e1a7839049b9b
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/30000
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Stephen White <senorblanco@chromium.org>
> Commit-Queue: Austin Eng <enga@chromium.org>

Bug: chromium:951558
Change-Id: I827cdbd212fa585b542fd4ea1eb9654eec6002c7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/30420
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn_wire/client/Client.cpp

@@ -19,6 +19,30 @@
 
 namespace dawn_wire { namespace client {
 
+    namespace {
+
+        class NoopCommandSerializer final : public CommandSerializer {
+          public:
+            static NoopCommandSerializer* GetInstance() {
+                static NoopCommandSerializer gNoopCommandSerializer;
+                return &gNoopCommandSerializer;
+            }
+
+            ~NoopCommandSerializer() = default;
+
+            size_t GetMaximumAllocationSize() const final {
+                return 0;
+            }
+            void* GetCmdSpace(size_t size) final {
+                return nullptr;
+            }
+            bool Flush() final {
+                return false;
+            }
+        };
+
+    }  // anonymous namespace
+
     Client::Client(CommandSerializer* serializer, MemoryTransferService* memoryTransferService)
         : ClientBase(), mSerializer(serializer), mMemoryTransferService(memoryTransferService) {
         if (mMemoryTransferService == nullptr) {
@@ -53,11 +77,7 @@ namespace dawn_wire { namespace client {
     }
 
     void Client::Disconnect() {
-        if (mDisconnected) {
-            return;
-        }
-
-        mDisconnected = true;
+        mSerializer = ChunkedCommandSerializer(NoopCommandSerializer::GetInstance());
         if (mDevice != nullptr) {
             mDevice->HandleDeviceLost("GPU connection lost");
         }

src/dawn_wire/client/Client.h

@@ -48,10 +48,6 @@ namespace dawn_wire { namespace client {
 
         template <typename Cmd>
         void SerializeCommand(const Cmd& cmd) {
-            // TODO(enga): Swap out the serializer with a no-op one on disconnect.
-            if (mDisconnected) {
-                return;
-            }
             mSerializer.SerializeCommand(cmd, *this);
         }
 
@@ -59,10 +55,6 @@ namespace dawn_wire { namespace client {
         void SerializeCommand(const Cmd& cmd,
                               size_t extraSize,
                               ExtraSizeSerializeFn&& SerializeExtraSize) {
-            // TODO(enga): Swap out the serializer with a no-op one on disconnect.
-            if (mDisconnected) {
-                return;
-            }
             mSerializer.SerializeCommand(cmd, *this, extraSize, SerializeExtraSize);
         }
 
@@ -76,7 +68,6 @@ namespace dawn_wire { namespace client {
         WireDeserializeAllocator mAllocator;
         MemoryTransferService* mMemoryTransferService = nullptr;
         std::unique_ptr<MemoryTransferService> mOwnedMemoryTransferService = nullptr;
-        bool mDisconnected = false;
     };
 
     std::unique_ptr<MemoryTransferService> CreateInlineMemoryTransferService();