Fix some editor tests to actually change something instead of throwing.

editor/libeditor/html/crashtests/448329-1.html

@@ -15,6 +15,9 @@ function test448329(id,cmd) {
   var doc = elm.contentDocument;
   doc.designMode = "On";
 
+  // Work around getSelection depending on a presshell but not flushing to get
+  // one.
+  doc.body.offsetWidth;
   var s = doc.defaultView.getSelection();
 
   // Test document node

editor/libeditor/html/crashtests/448329-3.html

@@ -15,6 +15,9 @@ function test448329(id,cmd,val) {
   var doc = elm.contentDocument;
   doc.designMode = "On";
 
+  // Work around getSelection depending on a presshell but not flushing to get
+  // one.
+  doc.body.offsetWidth;
   var s = doc.defaultView.getSelection();
 
   // Test document node

editor/libeditor/html/crashtests/crashtests.list

@@ -8,7 +8,7 @@ load 428489-1.html
 load 431086-1.xhtml
 load 448329-1.html
 load 448329-2.html
-load 448329-3.html
+asserts(16) load 448329-3.html
 load 456727-1.html
 load 456727-2.html
 asserts(1) load 467647-1.html # bug 382210