Simplify Fantom test

packages/react-native-fantom/src/__tests__/Fantom-itest.js

@@ -25,22 +25,11 @@ function getActualViewportDimensions(root: Root): {
   viewportWidth: number,
   viewportHeight: number,
 } {
-  let maybeNode;
-
   Fantom.runTask(() => {
-    root.render(
-      <View
-        style={{width: '100%', height: '100%'}}
-        ref={node => {
-          maybeNode = node;
-        }}
-      />,
-    );
+    root.render(<View />);
   });
 
-  const node = ensureInstance(maybeNode, ReactNativeElement);
-
-  const rect = node.getBoundingClientRect();
+  const rect = root.document.documentElement.getBoundingClientRect();
   return {
     viewportWidth: rect.width,
     viewportHeight: rect.height,

packages/react-native/src/private/webapis/dom/nodes/__tests__/ReactNativeDocument-itest.js

@@ -125,6 +125,32 @@ describe('ReactNativeDocument', () => {
     expect(document.textContent).toBe(null);
   });
 
+  it('provides a documentElement node that behaves like a regular element', () => {
+    let lastNode;
+
+    const root = Fantom.createRoot({viewportWidth: 200, viewportHeight: 100});
+    Fantom.runTask(() => {
+      root.render(
+        <View
+          ref={node => {
+            lastNode = node;
+          }}
+        />,
+      );
+    });
+
+    const element = ensureInstance(lastNode, ReactNativeElement);
+    const document = ensureInstance(element.ownerDocument, ReactNativeDocument);
+
+    const {x, y, width, height} =
+      document.documentElement.getBoundingClientRect();
+
+    expect(x).toBe(0);
+    expect(y).toBe(0);
+    expect(width).toBe(200);
+    expect(height).toBe(100);
+  });
+
   it('implements compareDocumentPosition correctly', () => {
     let lastNode;
 

packages/react-native/src/private/webapis/dom/nodes/internals/NodeInternals.js

@@ -129,6 +129,12 @@ export function getNativeElementReference(
   // $FlowExpectedError[incompatible-cast] We know ReadOnlyElement instances provide InternalInstanceHandle
   const instanceHandle = getInstanceHandle(node) as InternalInstanceHandle;
 
+  if (isReactNativeDocumentElementInstanceHandle(instanceHandle)) {
+    return getNativeElementReferenceFromReactNativeDocumentElementInstanceHandle(
+      instanceHandle,
+    );
+  }
+
   // $FlowExpectedError[incompatible-return]
   return getRendererProxy().getNodeFromInternalInstanceHandle(instanceHandle);
 }