Support InlineSpan as customRender

Same as #298 but only the minimal required changes to make this work

Author: erickok

example/lib/main.dart

@@ -81,7 +81,7 @@ const htmlData = """
       <tr><td>fData</td><td>fData</td><td>fData</td></tr>
       </tfoot>
       </table>
-      <h3>Custom Element Support:</h3>
+      <h3>Custom Element Support (inline: <bird></bird> and as block):</h3>
       <flutter></flutter>
       <flutter horizontal></flutter>
       <h3>SVG support:</h3>
@@ -122,7 +122,6 @@ const htmlData = """
       <p>
         <img alt='Google' src='https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_92x30dp.png' />
         <a href='https://google.com'><img alt='Google' src='https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_92x30dp.png' /></a>
-        <img alt='Alt Text of an intentionally broken image' src='https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_92x30d' />
       </p>
       <h3>Video support:</h3>
       <video controls>
@@ -173,6 +172,9 @@ class _MyHomePageState extends State<MyHomePage> {
             "var": Style(fontFamily: 'serif'),
           },
           customRender: {
+            "bird": (RenderContext context, Widget child, attributes, _) {
+              return TextSpan(text: "🐦");
+            },
             "flutter": (RenderContext context, Widget child, attributes, _) {
               return FlutterLogo(
                 style: (attributes['horizontal'] != null)

lib/html_parser.dart

@@ -15,7 +15,7 @@ import 'package:html/parser.dart' as htmlparser;
 import 'package:webview_flutter/webview_flutter.dart';
 
 typedef OnTap = void Function(String url);
-typedef CustomRender = Widget Function(
+typedef CustomRender = dynamic Function(
   RenderContext context,
   Widget parsedChild,
   Map<String, String> attributes,
@@ -243,27 +243,31 @@ class HtmlParser extends StatelessWidget {
     );
 
     if (customRender?.containsKey(tree.name) ?? false) {
-      return WidgetSpan(
-        child: ContainerSpan(
+      final render = customRender[tree.name].call(
+        newContext,
+        ContainerSpan(
           newContext: newContext,
           style: tree.style,
           shrinkWrap: context.parser.shrinkWrap,
-          child: customRender[tree.name].call(
-            newContext,
-            ContainerSpan(
-              newContext: newContext,
-              style: tree.style,
-              shrinkWrap: context.parser.shrinkWrap,
-              children: tree.children
-                      ?.map((tree) => parseTree(newContext, tree))
-                      ?.toList() ??
-                  [],
-            ),
-            tree.attributes,
-            tree.element,
-          ),
+          children: tree.children
+                  ?.map((tree) => parseTree(newContext, tree))
+                  ?.toList() ??
+              [],
         ),
+        tree.attributes,
+        tree.element,
       );
+      assert(render is InlineSpan || render is Widget);
+      return render is InlineSpan
+          ? render
+          : WidgetSpan(
+              child: ContainerSpan(
+                newContext: newContext,
+                style: tree.style,
+                shrinkWrap: context.parser.shrinkWrap,
+                child: render,
+              ),
+            );
     }
 
     //Return the correct InlineSpan based on the element type.