Implement :valid and :invalid pseudoclass for <form> (resubmitting)

LayoutTests/fast/forms/form-pseudo-valid-style-expected.txt

Index: LayoutTests/fast/forms/form-pseudo-valid-style-expected.txt
diff --git a/LayoutTests/fast/forms/form-pseudo-valid-style-expected.txt b/LayoutTests/fast/forms/form-pseudo-valid-style-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..14ecf3480e3ff858e27e5627e01f682f97cfdcea
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+++ b/LayoutTests/fast/forms/form-pseudo-valid-style-expected.txt
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+Check if :valid/:invalid CSS pseudo selectors are lively applied for forms
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+Removing and adding required text inputs and modifying ther value by a DOM tree mutation:
+PASS backgroundOf(form1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+PASS form1.removeChild(input1); backgroundOf(form1) is validColor
+PASS backgroundOf(sub1) is subValidColor
+PASS form1.appendChild(input1); backgroundOf(form1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+PASS input1.setAttribute("value", "a"); backgroundOf(form1) is validColor
+PASS backgroundOf(sub1) is subValidColor
+PASS input2.setAttribute("value", ""); backgroundOf(form1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+
+Adding a required text input that is not a direct child of the form:
+PASS backgroundOf(form1) is validColor
+PASS div1.appendChild(input1); backgroundOf(form1) is invalidColor
+
+Render multiple forms and move an invalid input from one to another:
+PASS backgroundOf($("form1")) is invalidColor
+PASS backgroundOf($("form2")) is validColor
+PASS backgroundOf($("form3")) is validColor
+PASS backgroundOf($("form1")) is validColor
+PASS backgroundOf($("form3")) is invalidColor
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+