Update navigator.Share to use GetTopLevelRenderWidgetHostView

Future-proofing the Windows implementation of navigator.Share to fetch
the top-level RenderWidgetHostView (when attempting to find the HWND
designated for accessibility with the WebContents). This does not impact
any known scenarios today, but would if the WebContents were ever
hosted in a RenderWidgetHostViewChildFrame.

Change-Id: Ie1692498a5481a68a39f88a6d72e2fd5b8a415f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3812389
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Hoch Hochkeppel <mhochk@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1032034}

chrome/browser/webshare/win/share_operation.cc

@@ -434,7 +434,7 @@ void ShareOperation::Run(blink::mojom::ShareService::ShareCallback callback) {
   // with the WebContents.
   HWND hwnd = nullptr;
   content::RenderWidgetHostView* host_view =
-      web_contents_->GetRenderWidgetHostView();
+      web_contents_->GetTopLevelRenderWidgetHostView();
   if (host_view) {
     ui::AXPlatformNode* platform_node =
         ui::AXPlatformNode::FromNativeViewAccessible(