Make the check for calling super.created not sensitive to line delimiters

tools/dom/templates/html/impl/impl_HTMLDocument.darttemplate

Index: tools/dom/templates/html/impl/impl_HTMLDocument.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_HTMLDocument.darttemplate b/tools/dom/templates/html/impl/impl_HTMLDocument.darttemplate
index 6d3ecc34e18e46c006b1f438b4ee7a9ded82a8b0..3c6e3a477af78433d746098537ffe098b717917a 100644
--- a/tools/dom/templates/html/impl/impl_HTMLDocument.darttemplate
+++ b/tools/dom/templates/html/impl/impl_HTMLDocument.darttemplate
@@ -282,10 +282,8 @@ $if DARTIUM
 
         // Get the created constructor source and look at the initializer;
         // Must call super.created() if not its as an error.
-        var createdSource = methodMirror.source?.replaceAll('\n', ' ');
-        RegExp regExp = new RegExp(r":(.*?)(;|}|\n)");
-        var match = regExp.firstMatch(createdSource);
-        superCreatedCalled = match.input.substring(match.start,match.end).contains("super.created(");
+        var createdSource = methodMirror.source;
+        superCreatedCalled = createdSource.contains("super.created(");
       }
 
       if (!superCreatedCalled) {
@@ -400,7 +398,7 @@ $else
       //
       //              See https://github.com/dart-lang/sdk/issues/23666
       int creating = 0;
-      // TODO(jacobr): warning: 
+      // TODO(jacobr): warning:
       elemProto['createdCallback'] = js.JsNative.withThis(($this) {
         if (_getJSClassName(reflectClass(customElementClass).superclass) != null && creating < 2) {
           creating++;
@@ -415,7 +413,7 @@ $else
           } finally {
             // Need to remember the Dart class that was created for this custom so
             // return it and setup the blink_jsObject to the $this that we'll be working
-            // with as we talk to blink. 
+            // with as we talk to blink.
             js.setDartHtmlWrapperFor($this, dartClass);
 
             creating--;