Serialize Text nodes for HTML fragments correctly

Serialize Text nodes for HTML fragments correctly as described in the spec:
https://html.spec.whatwg.org/#serialising-html-fragments

Bug: 651762
TEST=external/wpt/html/syntax/serializing-html-fragments/serializing.html

Change-Id: Ib9e66b04caa82b366cf1c0f846ed9c597cba74a9
Reviewed-on: https://chromium-review.googlesource.com/886646
Commit-Queue: Rob Buis <rob.buis@samsung.com>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532302}

third_party/WebKit/Source/core/editing/serializers/MarkupFormatter.cpp

@@ -474,8 +474,13 @@ EntityMask MarkupFormatter::EntityMaskForText(const Text& text) const {
   if (text.parentElement())
     parent_name = &(text.parentElement())->TagQName();
 
-  if (parent_name && (*parent_name == scriptTag || *parent_name == styleTag ||
-                      *parent_name == xmpTag))
+  if (parent_name &&
+      (*parent_name == scriptTag || *parent_name == styleTag ||
+       *parent_name == xmpTag || *parent_name == iframeTag ||
+       *parent_name == plaintextTag || *parent_name == noembedTag ||
+       *parent_name == noframesTag ||
+       (*parent_name == noscriptTag &&
+        text.GetDocument().CanExecuteScripts(kNotAboutToExecuteScript))))
     return kEntityMaskInCDATA;
   return kEntityMaskInHTMLPCDATA;
 }