Revert of 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"
-
-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 equal(a.characters8(), b.characters8(), a.length());
-        return equal(a.characters8(), b.characters16(), a.length());
-    }
-    if (b.is8Bit())
-        return equal(a.characters16(), b.characters8(), a.length());
-    return equal(a.characters16(), b.characters16(), a.length());
-}
-
-} // namespace WTF