Add intentional optimization comment in Node::setTextContent

LayoutTests/fast/dom/Node/textContent-expected.txt

Index: LayoutTests/fast/dom/Node/textContent-expected.txt
diff --git a/LayoutTests/fast/dom/Node/textContent-expected.txt b/LayoutTests/fast/dom/Node/textContent-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..aa392a96e3d61e8e76a0c93ca6e1f776f0cf05ef
--- /dev/null
+++ b/LayoutTests/fast/dom/Node/textContent-expected.txt
@@ -0,0 +1,84 @@
+This is a testharness.js-based test.
+PASS For an empty Element, textContent should be the empty string 
+PASS For an empty DocumentFragment, textContent should be the empty string 
+PASS Element with children 
+PASS Element with descendants 
+PASS DocumentFragment with children 
+PASS DocumentFragment with descendants 
+PASS For an empty Text, textContent should be the empty string 
+PASS For an empty ProcessingInstruction, textContent should be the empty string 
+PASS For an empty Comment, textContent should be the empty string 
+PASS For a Text with data, textContent should be that data 
+PASS For a ProcessingInstruction with data, textContent should be that data 
+PASS For a Comment with data, textContent should be that data 
+PASS For Documents created by parser, textContent should be null 
+PASS For Documents created by createDocument, textContent should be null 
+PASS For Documents created by createHTMLDocument, textContent should be null 
+PASS For DocumentType created by parser, textContent should be null 
+PASS For DocumentType created by script, textContent should be null 
+PASS Element without children set to null 
+PASS Element with empty text node as child set to null 
+PASS Element with children set to null 
+PASS Element with descendants set to null 
+PASS DocumentFragment without children set to null 
+PASS DocumentFragment with empty text node as child set to null 
+PASS DocumentFragment with children set to null 
+PASS DocumentFragment with descendants set to null 
+PASS Element without children set to undefined 
+PASS Element with empty text node as child set to undefined 
+PASS Element with children set to undefined 
+PASS Element with descendants set to undefined 
+PASS DocumentFragment without children set to undefined 
+PASS DocumentFragment with empty text node as child set to undefined 
+PASS DocumentFragment with children set to undefined 
+PASS DocumentFragment with descendants set to undefined 
+PASS Element without children set to "" 
+FAIL Element with empty text node as child set to "" assert_equals: expected null but got Text node ""
+PASS Element with children set to "" 
+PASS Element with descendants set to "" 
+PASS DocumentFragment without children set to "" 
+FAIL DocumentFragment with empty text node as child set to "" assert_equals: expected null but got Text node ""
+PASS DocumentFragment with children set to "" 
+PASS DocumentFragment with descendants set to "" 
+PASS Element without children set to 42 
+PASS Element with empty text node as child set to 42 
+PASS Element with children set to 42 
+PASS Element with descendants set to 42 
+PASS DocumentFragment without children set to 42 
+PASS DocumentFragment with empty text node as child set to 42 
+PASS DocumentFragment with children set to 42 
+PASS DocumentFragment with descendants set to 42 
+PASS Element without children set to "abc" 
+PASS Element with empty text node as child set to "abc" 
+PASS Element with children set to "abc" 
+PASS Element with descendants set to "abc" 
+PASS DocumentFragment without children set to "abc" 
+PASS DocumentFragment with empty text node as child set to "abc" 
+PASS DocumentFragment with children set to "abc" 
+PASS DocumentFragment with descendants set to "abc" 
+PASS Element without children set to "<b>xyz</b>" 
+PASS Element with empty text node as child set to "<b>xyz</b>" 
+PASS Element with children set to "<b>xyz</b>" 
+PASS Element with descendants set to "<b>xyz</b>" 
+PASS DocumentFragment without children set to "<b>xyz</b>" 
+PASS DocumentFragment with empty text node as child set to "<b>xyz</b>" 
+PASS DocumentFragment with children set to "<b>xyz</b>" 
+PASS DocumentFragment with descendants set to "<b>xyz</b>" 
+PASS Element without children set to "d\0e" 
+PASS Element with empty text node as child set to "d\0e" 
+PASS Element with children set to "d\0e" 
+PASS Element with descendants set to "d\0e" 
+PASS DocumentFragment without children set to "d\0e" 
+PASS DocumentFragment with empty text node as child set to "d\0e" 
+PASS DocumentFragment with children set to "d\0e" 
+PASS DocumentFragment with descendants set to "d\0e" 
+PASS For a Text, textContent should set the data 
+PASS For a ProcessingInstruction, textContent should set the data 
+PASS For a Comment, textContent should set the data 
+PASS For Documents created by parser, setting textContent should do nothing 
+PASS For Documents created by createDocument, setting textContent should do nothing 
+PASS For Documents created by createHTMLDocument, setting textContent should do nothing 
+PASS For DocumentType created by parser, setting textContent should do nothing 
+PASS For DocumentType created by script, setting textContent should do nothing 
+Harness: the test ran to completion.
+