Expand WTF::StringView's API to be more like StringPiece.

third_party/WebKit/Source/wtf/text/StringView.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 "wtf/text/StringView.h"
+
+#include "wtf/text/StringImpl.h"
+#include "wtf/text/WTFString.h"
+
+namespace WTF {
+
+StringView::StringView(const UChar* chars, unsigned length)
+    : m_length(length)
+    , m_is8Bit(false)
+{
+    SECURITY_DCHECK(!chars || length <= lengthOfNullTerminatedString(chars));
+    m_data.characters16 = chars;
+}
+
+StringView::StringView(const UChar* chars)
+    : StringView(chars, chars ? lengthOfNullTerminatedString(chars) : 0) {}
+
+#if DCHECK_IS_ON()
+StringView::~StringView()
+{
+    // StringView does not own the StringImpl, we must not be the last ref.
+    DCHECK(!m_impl || !m_impl->hasOneRef());
+}
+#endif
+
+String StringView::toString() const
+{
+    if (isNull())
+        return String();
+    if (isEmpty())
+        return emptyString();
+    if (is8Bit())
+        return String(m_data.characters8, m_length);
+    return String(m_data.characters16, m_length);
+}
+
+bool equalStringView(const StringView& a, const StringView& b)
+{
+    if (a.length() != b.length())
+        return false;
+    if (a.isEmpty() || b.isEmpty())
+        return a.isEmpty() == b.isEmpty();
+    if (a.is8Bit()) {
+        if (b.is8Bit())
+            return WTF::equal(a.characters8(), b.characters8(), a.length());

[Yuta Kitamura, 2016/05/27 04:47:41]

nit: Omit "WTF::".

+        return WTF::equal(a.characters8(), b.characters16(), a.length());
+    }
+    if (b.is8Bit())
+        return WTF::equal(a.characters16(), b.characters8(), a.length());
+    return WTF::equal(a.characters16(), b.characters16(), a.length());
+}
+
+} // namespace WTF