Improve <textarea> validation performance.

HTMLTextAreaElement::value() is a costly operation, and we can avoid it
if a <textarea> has neither 'required' attribute nor 'maxlength' attribute.

This CL improves PerformanceTests/DOM/textarea-dom.html and
textarea-edit.html by a few percent.

BUG=

Review URL: https://codereview.chromium.org/543403003

git-svn-id: svn://svn.chromium.org/blink/trunk@181785 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/html/HTMLTextAreaElement.cpp

@@ -490,15 +490,22 @@ String HTMLTextAreaElement::validationMessage() const
 
 bool HTMLTextAreaElement::valueMissing() const
 {
-    return willValidate() && valueMissing(value());
+    // We should not call value() for performance.
+    return willValidate() && valueMissing(0);
+}
+
+bool HTMLTextAreaElement::valueMissing(const String* value) const
+{
+    return isRequiredFormControl() && !isDisabledOrReadOnly() && (value ? *value : this->value()).isEmpty();
 }
 
 bool HTMLTextAreaElement::tooLong() const
 {
-    return willValidate() && tooLong(value(), CheckDirtyFlag);
+    // We should not call value() for performance.
+    return willValidate() && tooLong(0, CheckDirtyFlag);
 }
 
-bool HTMLTextAreaElement::tooLong(const String& value, NeedsToCheckDirtyFlag check) const
+bool HTMLTextAreaElement::tooLong(const String* value, NeedsToCheckDirtyFlag check) const
 {
     // Return false for the default value or value set by script even if it is
     // longer than maxLength.
@@ -508,12 +515,12 @@ bool HTMLTextAreaElement::tooLong(const String& value, NeedsToCheckDirtyFlag che
     int max = maxLength();
     if (max < 0)
         return false;
-    return computeLengthForSubmission(value) > static_cast<unsigned>(max);
+    return computeLengthForSubmission(value ? *value : this->value()) > static_cast<unsigned>(max);
 }
 
 bool HTMLTextAreaElement::isValidValue(const String& candidate) const
 {
-    return !valueMissing(candidate) && !tooLong(candidate, IgnoreDirtyFlag);
+    return !valueMissing(&candidate) && !tooLong(&candidate, IgnoreDirtyFlag);
 }
 
 void HTMLTextAreaElement::accessKeyAction(bool)

third_party/WebKit/Source/core/html/HTMLTextAreaElement.h

@@ -121,8 +121,9 @@ private:
     virtual bool matchesReadOnlyPseudoClass() const OVERRIDE;
     virtual bool matchesReadWritePseudoClass() const OVERRIDE;
 
-    bool valueMissing(const String& value) const { return isRequiredFormControl() && !isDisabledOrReadOnly() && value.isEmpty(); }
-    bool tooLong(const String&, NeedsToCheckDirtyFlag) const;
+    // If the String* argument is 0, apply this->value().
+    bool valueMissing(const String*) const;
+    bool tooLong(const String*, NeedsToCheckDirtyFlag) const;
 
     int m_rows;
     int m_cols;