Reintroduce password support to NativeTextfieldViews

ui/base/text/utf16_indexing.cc

+// Copyright (c) 2012 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 "ui/base/text/utf16_indexing.h"
+
+#include "base/logging.h"
+#include "base/third_party/icu/icu_utf.h"
+
+namespace ui {
+
+bool IsValidCodePointIndex(const string16& s, size_t index) {
+  return index == 0 || index == s.length() ||
+    !(CBU16_IS_TRAIL(s[index]) && CBU16_IS_LEAD(s[index - 1]));
+}
+
+ptrdiff_t UTF16IndexToOffset(const string16& s, size_t base, size_t pos) {
+  // The indices point between UTF-16 words (range 0 to s.length() inclusive).
+  // In order to consistently handle indices that point to the middle of a
+  // surrogate pair, we count the first word in that surrogate pair and not
+  // the second. The test "s[i] is not the second half of a surrogate pair" is
+  // "IsValidCodePointIndex(s, i)".
+  DCHECK_LE(base, s.length());
+  DCHECK_LE(pos, s.length());
+  ptrdiff_t delta = 0;
+  while (base < pos)
+    delta += IsValidCodePointIndex(s, base++) ? 1 : 0;
+  while (pos < base)
+    delta -= IsValidCodePointIndex(s, pos++) ? 1 : 0;
+  return delta;
+}
+
+size_t UTF16OffsetToIndex(const string16& s, size_t base, ptrdiff_t offset) {
+  DCHECK_LE(base, s.length());
+  // As in UTF16IndexToOffset, we count the first half of a surrogate pair, not
+  // the second. When stepping from pos to pos+1 we check s[pos:pos+1] == s[pos]
+  // (Python syntax), hence pos++. When stepping from pos to pos-1 we check
+  // s[pos-1], hence --pos.
+  size_t pos = base;
+  while (offset > 0 && pos < s.length())
+    offset -= IsValidCodePointIndex(s, pos++) ? 1 : 0;
+  while (offset < 0 && pos > 0)
+    offset += IsValidCodePointIndex(s, --pos) ? 1 : 0;
+  // If offset != 0 then we ran off the edge of the string, which is a contract
+  // violation but is handled anyway (by clamping) in release for safety.
+  DCHECK_EQ(offset, 0);
+  // Since the second half of a surrogate pair has "length" zero, there is an
+  // ambiguity in the returned position. Resolve it by always returning a valid
+  // index.
+  if (!IsValidCodePointIndex(s, pos))
+    ++pos;
+  return pos;
+}
+
+}  // namespace ui