Implement :valid and :invalid pseudoclass for <fieldset>

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

Index: LayoutTests/fast/forms/fieldset-pseudo-valid-style-expected.txt
diff --git a/LayoutTests/fast/forms/fieldset-pseudo-valid-style-expected.txt b/LayoutTests/fast/forms/fieldset-pseudo-valid-style-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..99cce9ad75e6527040b5afb6e3be490985a4cc15
--- /dev/null
+++ b/LayoutTests/fast/forms/fieldset-pseudo-valid-style-expected.txt
@@ -0,0 +1,48 @@
+Check if :valid/:invalid CSS pseudo selectors are lively applied for fieldsets
+
+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(fieldset1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+PASS fieldset1.removeChild(input1); backgroundOf(fieldset1) is validColor
+PASS backgroundOf(sub1) is subValidColor
+PASS fieldset1.appendChild(input1); backgroundOf(fieldset1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+PASS input1.setAttribute("value", "a"); backgroundOf(fieldset1) is validColor
+PASS backgroundOf(sub1) is subValidColor
+PASS input2.setAttribute("value", ""); backgroundOf(fieldset1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+
+Adding a required text input that is not a direct child of the fieldset:
+PASS backgroundOf(fieldset1) is validColor
+PASS div1.appendChild(input1); backgroundOf(fieldset1) is invalidColor
+
+Nested fieldsets:
+PASS backgroundOf($("fieldset0")) is invalidColor
+PASS backgroundOf($("fieldset1")) is invalidColor
+PASS backgroundOf($("fieldset2")) is validColor
+PASS input1.setAttribute("value", "v"); backgroundOf($("fieldset0")) is validColor
+PASS backgroundOf($("fieldset1")) is validColor
+PASS backgroundOf($("fieldset2")) is validColor
+PASS input2.setAttribute("required", ""); backgroundOf($("fieldset0")) is invalidColor
+PASS backgroundOf($("fieldset1")) is validColor
+PASS backgroundOf($("fieldset2")) is invalidColor
+
+Render multiple fieldsets and move an invalid input from one to another:
+PASS backgroundOf($("fieldset1")) is invalidColor
+PASS backgroundOf($("fieldset2")) is validColor
+PASS backgroundOf($("fieldset3")) is validColor
+PASS backgroundOf($("fieldset1")) is validColor
+PASS backgroundOf($("fieldset3")) is invalidColor
+
+Ensure that invalid event was not triggered on style evaluation:
+PASS backgroundOf(fieldset1) is invalidColor
+PASS val is "0"
+PASS input1.checkValidity(); val is "1"
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+