Add the last usage serial in Buffer

Add the last usage serial in Buffer, it is used for optimizing
MapAsync(), so the callback of MapAsync() is called when the last usage
serial is done instead of using the current pending serial when
the MapAsync() is called.

Bug: b/265151060
Change-Id: Ibc95d4e41d41896f0a49b0fd1068912b46ea14e1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/116693
Commit-Queue: Peng Huang <penghuang@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn/native/opengl/BufferGL.cpp

@@ -39,6 +39,8 @@ ResultOrError<Ref<Buffer>> Buffer::CreateInternalBuffer(Device* device,
 
 Buffer::Buffer(Device* device, const BufferDescriptor* descriptor)
     : BufferBase(device, descriptor) {
+    // TODO(penghuang): track usage for GL.
+    mLastUsageSerial = kMaxExecutionSerial;
     const OpenGLFunctions& gl = device->GetGL();
     // Allocate at least 4 bytes so clamped accesses are always in bounds.
     mAllocatedSize = std::max(GetSize(), uint64_t(4u));