Fix bug where form/fieldset :valid/:invalid won't be recalculated upon control's willValidate change

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
index 99cce9ad75e6527040b5afb6e3be490985a4cc15..a38eefa027692a2c6f998dbbe4f2e644bf0abdcf 100644
--- a/LayoutTests/fast/forms/fieldset-pseudo-valid-style-expected.txt
+++ b/LayoutTests/fast/forms/fieldset-pseudo-valid-style-expected.txt
@@ -3,7 +3,7 @@ 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:
+Removing and adding required text inputs and modifying their value by a DOM tree mutation:
 PASS backgroundOf(fieldset1) is invalidColor
 PASS backgroundOf(sub1) is subInvalidColor
 PASS fieldset1.removeChild(input1); backgroundOf(fieldset1) is validColor
@@ -15,6 +15,16 @@ PASS backgroundOf(sub1) is subValidColor
 PASS input2.setAttribute("value", ""); backgroundOf(fieldset1) is invalidColor
 PASS backgroundOf(sub1) is subInvalidColor
 
+Disabling and marking inputs readonly by a DOM tree mutation:
+PASS backgroundOf(fieldset1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+PASS input1.disabled=1; backgroundOf(fieldset1) is validColor
+PASS backgroundOf(sub1) is subValidColor
+PASS input1.disabled=0; backgroundOf(fieldset1) is invalidColor
+PASS backgroundOf(sub1) is subInvalidColor
+PASS input1.setAttribute("readonly", "1"); backgroundOf(fieldset1) is validColor
+PASS backgroundOf(sub1) is subValidColor
+
 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