dawn/node: Implement GPUBuffer.getMapState()

Bug: dawn:1761
Change-Id: Id01789a2df8afd5726f6fc776e7d825153fd0f85
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/127722
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

src/dawn/node/binding/Converter.cpp

@@ -1722,6 +1722,21 @@ bool Converter::Convert(interop::GPUQueryType& out, wgpu::QueryType in) {
     return false;
 }
 
+bool Convert(interop::GPUBufferMapState& out, wgpu::BufferMapState in) {
+    switch (in) {
+        case wgpu::BufferMapState::Unmapped:
+            out = interop::GPUBufferMapState::kUnmapped;
+            return true;
+        case wgpu::BufferMapState::Pending:
+            out = interop::GPUBufferMapState::kPending;
+            return true;
+        case wgpu::BufferMapState::Mapped:
+            out = interop::GPUBufferMapState::kMapped;
+            return true;
+    }
+    return false;
+}
+
 bool Converter::Convert(wgpu::AddressMode& out, const interop::GPUAddressMode& in) {
     out = wgpu::AddressMode::Repeat;
     switch (in) {

src/dawn/node/binding/Converter.h

@@ -270,6 +270,8 @@ class Converter {
 
     [[nodiscard]] bool Convert(interop::GPUQueryType& out, wgpu::QueryType in);
 
+    [[nodiscard]] bool Convert(interop::GPUBufferMapState& out, wgpu::BufferMapState in);
+
     // The two conversion methods don't generate an error when false is returned. That
     // responsibility is left to the caller if it is needed (it isn't always needed, see
     // https://gpuweb.github.io/gpuweb/#gpu-supportedfeatures)

src/dawn/node/binding/GPUBuffer.cpp

@@ -166,8 +166,17 @@ interop::GPUSize64 GPUBuffer::getSize(Napi::Env) {
     return buffer_.GetSize();
 }
 
-interop::GPUBufferMapState GPUBuffer::getMapState(Napi::Env) {
-    UNIMPLEMENTED();
+interop::GPUBufferMapState GPUBuffer::getMapState(Napi::Env env) {
+    interop::GPUBufferMapState result;
+
+    Converter conv(env);
+    if (!conv(result, buffer_.GetMapState())) {
+        Napi::Error::New(env, "Couldn't convert usage to a JavaScript value.")
+            .ThrowAsJavaScriptException();
+        return interop::GPUBufferMapState::kUnmapped;
+    }
+
+    return result;
 }
 
 interop::GPUBufferUsageFlags GPUBuffer::getUsage(Napi::Env env) {