dawn/wire: Move all the members of `WriteHandle` to private

This patch moves all the members of `WriteHandle` to private after
the land of the related changes in Chromium. Because `mTargetData`
and `mDataLength` may not be set together, we cannot put them into
one `std::span`.

bug: 42240963
Change-Id: I13b0c46c09040820fbf19e92ef57d81624ceeece
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/256814
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

include/dawn/wire/WireServer.h

diff --git a/include/dawn/wire/WireServer.h b/include/dawn/wire/WireServer.h
index 19a269f..b6c0097 100644
--- a/include/dawn/wire/WireServer.h
+++ b/include/dawn/wire/WireServer.h
@@ -139,15 +139,12 @@
                                            size_t size) = 0;
         std::span<uint8_t> GetTarget() const;
 
-      protected:
-        // TODO(42240963): Move them into a std::span and put it to private after landing the
-        // related changes in Chromium.
-        void* mTargetData = nullptr;
-        size_t mDataLength = 0;
-
       private:
         WriteHandle(const WriteHandle&) = delete;
         WriteHandle& operator=(const WriteHandle&) = delete;
+
+        uint8_t* mTargetData = nullptr;
+        size_t mDataLength = 0;
     };
 
   private:

src/dawn/wire/WireServer.cpp

diff --git a/src/dawn/wire/WireServer.cpp b/src/dawn/wire/WireServer.cpp
index 3244a18..cf8b4eb 100644
--- a/src/dawn/wire/WireServer.cpp
+++ b/src/dawn/wire/WireServer.cpp
@@ -85,14 +85,14 @@
 MemoryTransferService::WriteHandle::~WriteHandle() = default;
 
 void MemoryTransferService::WriteHandle::SetTarget(void* data) {
-    mTargetData = data;
+    mTargetData = static_cast<uint8_t*>(data);
 }
 void MemoryTransferService::WriteHandle::SetDataLength(size_t dataLength) {
     mDataLength = dataLength;
 }
 std::span<uint8_t> MemoryTransferService::WriteHandle::GetTarget() const {
     DAWN_ASSERT(mTargetData != nullptr);
-    return std::span<uint8_t>(static_cast<uint8_t*>(mTargetData), mDataLength);
+    return std::span<uint8_t>(mTargetData, mDataLength);
 }
 
 }  // namespace server