fix: NativeImage serialization of <webview>.capturePage() result (#20825)

spec/webview-spec.js

@@ -1022,6 +1022,20 @@ describe('<webview> tag', function () {
     })
   })
 
+  describe('<webview>.capturePage()', () => {
+    it('returns a Promise with a NativeImage', async () => {
+      const src = 'data:text/html,%3Ch1%3EHello%2C%20World!%3C%2Fh1%3E'
+      await loadWebView(webview, { src })
+
+      const image = await webview.capturePage()
+      const imgBuffer = image.toPNG()
+
+      // Check the 25th byte in the PNG.
+      // Values can be 0,2,3,4, or 6. We want 6, which is RGB + Alpha
+      expect(imgBuffer[25]).to.equal(6)
+    })
+  })
+
   describe('<webview>.printToPDF()', () => {
     before(function () {
       if (!features.isPrintingEnabled()) {