Improve support for multiselect list box accessibility on Windows.

base/win/enum_variant.cc

Index: base/win/enum_variant.cc
===================================================================
--- base/win/enum_variant.cc	(revision 0)
+++ base/win/enum_variant.cc	(revision 0)
@@ -0,0 +1,83 @@
+// Copyright (c) 2011 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 "base/win/enum_variant.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+
+namespace base {
+namespace win {
+
+EnumVariant::EnumVariant(unsigned long count)
+    : items_(new VARIANT[count]),
+      count_(count),
+      current_index_(0) {
+}
+
+EnumVariant::~EnumVariant() {
+}
+
+VARIANT* EnumVariant::ItemAt(unsigned long index) {
+  DCHECK(index < count_);
+  return &items_[index];
+}
+
+ULONG STDMETHODCALLTYPE EnumVariant::AddRef() {
+  return IUnknownImpl::AddRef();
+}
+
+ULONG STDMETHODCALLTYPE EnumVariant::Release() {
+  return IUnknownImpl::Release();
+}
+
+STDMETHODIMP EnumVariant::QueryInterface(REFIID riid, void** ppv) {
+  if (riid == IID_IEnumVARIANT) {
+    *ppv = static_cast<IEnumVARIANT*>(this);
+    AddRef();
+    return S_OK;
+  }
+
+  return IUnknownImpl::QueryInterface(riid, ppv);
+}
+
+STDMETHODIMP EnumVariant::Next(ULONG requested_count,
+                               VARIANT* out_elements,
+                               ULONG* out_elements_received) {
+  unsigned long count = std::min(requested_count, count_ - current_index_);
+  for (unsigned long i = 0; i < count; ++i)
+    out_elements[i] = items_[current_index_ + i];
+  current_index_ += count;
+  *out_elements_received = count;
+
+  return (count == requested_count ? S_OK : S_FALSE);
+}
+
+STDMETHODIMP EnumVariant::Skip(ULONG skip_count) {
+  unsigned long count = skip_count;
+  if (current_index_ + count > count_)
+    count = count_ - current_index_;
+
+  current_index_ += count;
+  return (count == skip_count ? S_OK : S_FALSE);
+}
+
+STDMETHODIMP EnumVariant::Reset() {
+  current_index_ = 0;
+  return S_OK;
+}
+
+STDMETHODIMP EnumVariant::Clone(IEnumVARIANT** out_cloned_object) {
+  EnumVariant* other = new EnumVariant(count_);
+  if (count_ > 0)
+    memcpy(other->ItemAt(0), &items_[0], count_ * sizeof(VARIANT));
+  other->Skip(current_index_);
+  other->AddRef();
+  *out_cloned_object = other;
+  return S_OK;
+}
+
+}  // namespace win
+}  // namespace base