Implement minlength for <input> and <textarea>.

LayoutTests/fast/forms/ValidityState-tooLong-textarea.html

Index: LayoutTests/fast/forms/ValidityState-tooLong-textarea.html
diff --git a/LayoutTests/fast/forms/ValidityState-tooLong-textarea.html b/LayoutTests/fast/forms/ValidityState-tooLong-textarea.html
index c8cbb9c53a2ee03299fd70f46f4532726df2a1c7..280f410cb604ce292991d7e262da33e8b1af6d40 100644
--- a/LayoutTests/fast/forms/ValidityState-tooLong-textarea.html
+++ b/LayoutTests/fast/forms/ValidityState-tooLong-textarea.html
@@ -50,11 +50,19 @@ textarea.value = 'abcde';
 shouldBeFalse('textarea.validity.tooLong');
 
 debug('');
-debug('Disabled');
-textarea.disabled = true;
-shouldBeFalse('textarea.validity.tooLong');
-textarea.disabled = false;
+debug('Disabling makes the control valid');
+textarea.focus();
+textarea.setSelectionRange(5, 5);  // Move the cursor at the end.
+document.execCommand('delete');
+shouldBeTrue('textarea.validity.tooLong');
+shouldBeFalse('textarea.disabled = true; textarea.validity.tooLong');
+shouldBeTrue('textarea.disabled = false; textarea.validity.tooLong');
 
+// TODO: The grapheme test below doesn't do its job because initial value is
+// always valid. After making a modificaton to trigger validity check, one can
+// see that the test would fail, which possibly reveals a code issue.
+// Once this is figured out, implement a similar test in
+// ValidityState-tooShort-textarea.html
 debug('');
 debug('Grapheme length is not greater than maxLength though character length is greater');
 // fancyX should be treated as 1 grapheme.