Return a span for WriteHandle Source

Builds on the previous changes to WriteHandle to support bounds checking
and updates the public method to return a span instead of a separate
data/size. The data/size methods are still present, though now private,
because that's the only way we can properly overload them from Chromium.

Bug: 487522152
Change-Id: If276cf5961a33102673b37388ea31612d0010005
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/296376
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Brandon Jones <bajones@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>

include/dawn/wire/WireServer.h

diff --git a/include/dawn/wire/WireServer.h b/include/dawn/wire/WireServer.h
index ef3b31d..e0513ee 100644
--- a/include/dawn/wire/WireServer.h
+++ b/include/dawn/wire/WireServer.h
@@ -140,16 +140,20 @@
                                            size_t size) = 0;
         std::span<uint8_t> GetTarget() const;
 
+        std::span<uint8_t> GetSource() const {
+            return std::span<uint8_t>(GetSourceData(), GetSourceSize());
+        }
+
+      private:
+        WriteHandle(const WriteHandle&) = delete;
+        WriteHandle& operator=(const WriteHandle&) = delete;
+
         // Returns a direct pointer to the source data that will
         // be copied into Target in DeserializeDataUpdate if accessible, nullptr
         // otherwise.
         virtual uint8_t* GetSourceData() const { return nullptr; }
         virtual size_t GetSourceSize() const { return 0; }
 
-      private:
-        WriteHandle(const WriteHandle&) = delete;
-        WriteHandle& operator=(const WriteHandle&) = delete;
-
         uint8_t* mTargetData = nullptr;
         size_t mDataLength = 0;
     };

src/dawn/wire/server/ServerQueue.cpp

diff --git a/src/dawn/wire/server/ServerQueue.cpp b/src/dawn/wire/server/ServerQueue.cpp
index cf45a39..2d355f7 100644
--- a/src/dawn/wire/server/ServerQueue.cpp
+++ b/src/dawn/wire/server/ServerQueue.cpp
@@ -98,7 +98,7 @@
 
     // Try first to use GetSourceData if the memory transfer service implements
     // it. If so, we can avoid a copy.
-    std::span<uint8_t> source(writeHandle->GetSourceData(), writeHandle->GetSourceSize());
+    std::span<uint8_t> source = writeHandle->GetSource();
     if (!source.empty()) {
         if (source.size() < size) {
             return WireResult::FatalError;
@@ -171,7 +171,7 @@
 
     // Try first to use GetSourceData if the memory transfer service implements
     // it. If so, we can avoid a copy.
-    std::span<uint8_t> source(writeHandle->GetSourceData(), writeHandle->GetSourceSize());
+    std::span<uint8_t> source = writeHandle->GetSource();
     if (!source.empty()) {
         if (source.size() < dataSize) {
             return WireResult::FatalError;