Newline characters in pasted text are not counted correctly for textarea[maxlength].

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

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/html/HTMLTextAreaElement.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blink {
+
+TEST(HTMLTextAreaElementTest, SanitizeUserInputValue)
+{
+    UChar kLeadSurrogate = 0xD800;
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue("", 0));
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue("a", 0));
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue("\n", 0));
+    StringBuilder builder;
+    builder.append(kLeadSurrogate);
+    String leadSurrogate = builder.toString();
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue(leadSurrogate, 0));
+
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue("", 1));
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue(leadSurrogate, 1));
+    EXPECT_EQ("a", HTMLTextAreaElement::sanitizeUserInputValue("a", 1));
+    EXPECT_EQ("", HTMLTextAreaElement::sanitizeUserInputValue("\n", 1));
+    EXPECT_EQ("\n", HTMLTextAreaElement::sanitizeUserInputValue("\n", 2));
+
+    EXPECT_EQ("abc", HTMLTextAreaElement::sanitizeUserInputValue(String("abc") + leadSurrogate, 4));
+    EXPECT_EQ("a\nc", HTMLTextAreaElement::sanitizeUserInputValue("a\ncdef", 4));
+}
+
+} // namespace blink