WebGPU: Remove copy of DawnCommands before passing to dawn_wire

This copy was needed because dawn_wire did not previously support
volatile pointers.

Bug: dawn:230
Change-Id: Ib5baff5c3e5da129086c40ef5b22a6d840f9f65b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846657Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703897}

gpu/command_buffer/service/webgpu_decoder_impl.cc

@@ -636,8 +636,7 @@ error::Error WebGPUDecoderImpl::HandleDawnCommands(
 
   TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("gpu.dawn"),
                "WebGPUDecoderImpl::HandleDawnCommands", "bytes", size);
-  std::vector<char> commands(shm_commands, shm_commands + size);
-  if (!wire_server_->HandleCommands(commands.data(), size)) {
+  if (!wire_server_->HandleCommands(shm_commands, size)) {
     NOTREACHED();
     return error::kLostContext;
   }