Add MemoryTransfer interfaces to the wire

This patch adds MemoryTransfer client/server interfaces and
uses it to implement data transfers for buffer mapping.

This patch also provides a default "inline" implementation of
the MemoryTransfer which is used if the embedder does not
provide one on initialization.

Because implementations of MemoryTransfer perform their own
serialization, a skip_serialize option is added to WireCmd records.

Bug: dawn:156
Change-Id: I2fa035517628a3ad465b0bc18a6ffc477e2bd67f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/8642
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn_wire/client/Client.cpp

@@ -17,10 +17,16 @@
 
 namespace dawn_wire { namespace client {
 
-    Client::Client(CommandSerializer* serializer)
+    Client::Client(CommandSerializer* serializer, MemoryTransferService* memoryTransferService)
         : ClientBase(),
           mDevice(DeviceAllocator().New(this)->object.get()),
-          mSerializer(serializer) {
+          mSerializer(serializer),
+          mMemoryTransferService(memoryTransferService) {
+        if (mMemoryTransferService == nullptr) {
+            // If a MemoryTransferService is not provided, fall back to inline memory.
+            mOwnedMemoryTransferService = CreateInlineMemoryTransferService();
+            mMemoryTransferService = mOwnedMemoryTransferService.get();
+        }
     }
 
     Client::~Client() {