[html] update templates for code accidentally changed in the generated code

These were updated in the dart:html output code in
https://dart-review.googlesource.com/c/sdk/+/163681

We may want to look into adding a presubmit that let us notify developers when a
change was made in one place but not the other (similar to how we used to check
for sdk and sdk_nnbd in the past).

Change-Id: I280315a5bb07971d0c0077498eb3c59944db0650
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/164640
Reviewed-by: Srujan Gaddam <srujzs@google.com>

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

@@ -1390,7 +1390,7 @@ $endif
       contextElement = _parseDocument$NULLASSERT.createElement(tagName);
       _parseDocument$NULLASSERT.body$NULLASSERT.append(contextElement);
     }
-    var fragment;
+    DocumentFragment fragment;
     if (Range.supportsCreateContextualFragment &&
         _canBeUsedToCreateContextualFragment) {
       _parseRange$NULLASSERT.selectNodeContents(contextElement);

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

@@ -24,7 +24,7 @@ $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS
           'version and onUpgradeNeeded must be specified together'));
     }
     try {
-      var request;
+      OpenDBRequest request;
       if (version != null) {
         request = _open(name, version);
       } else {