Re-land: Implement NativeViewAccessibilityWin using AXPlatformNodeWin.

ui/accessibility/platform/ax_platform_node_win.cc

+// Copyright 2015 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 <atlbase.h>
+#include <atlcom.h>
+#include <oleacc.h>
+
+#include "base/containers/hash_tables.h"
+#include "base/lazy_instance.h"
+#include "base/win/scoped_comptr.h"
+#include "third_party/iaccessible2/ia2_api_all.h"
+#include "ui/accessibility/ax_node_data.h"
+#include "ui/accessibility/ax_text_utils.h"
+#include "ui/accessibility/platform/ax_platform_node_delegate.h"
+#include "ui/accessibility/platform/ax_platform_node_win.h"
+#include "ui/base/win/atl_module.h"
+
+//
+// Macros to use at the top of any AXPlatformNodeWin function that implements
+// a COM interface. Because COM objects are reference counted and clients
+// are completely untrusted, it's important to always first check that our
+// object is still valid, and then check that all pointer arguments are
+// not NULL.
+//
+
+#define COM_OBJECT_VALIDATE() \
+    if (!delegate_) \
+      return E_FAIL;
+#define COM_OBJECT_VALIDATE_1_ARG(arg) \
+    if (!delegate_) return E_FAIL; \
+    if (!arg) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_2_ARGS(arg1, arg2) \
+    if (!delegate_) return E_FAIL; \
+    if (!arg1) return E_INVALIDARG; \
+    if (!arg2) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_3_ARGS(arg1, arg2, arg3) \
+    if (!delegate_) return E_FAIL; \
+    if (!arg1) return E_INVALIDARG; \
+    if (!arg2) return E_INVALIDARG; \
+    if (!arg3) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_4_ARGS(arg1, arg2, arg3, arg4) \
+    if (!delegate_) return E_FAIL; \
+    if (!arg1) return E_INVALIDARG; \
+    if (!arg2) return E_INVALIDARG; \
+    if (!arg3) return E_INVALIDARG; \
+    if (!arg4) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_VAR_ID(var_id) \
+    if (!delegate_) return E_FAIL; \
+    if (!IsValidId(var_id)) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, arg) \
+    if (!delegate_) return E_FAIL; \
+    if (!IsValidId(var_id)) return E_INVALIDARG; \
+    if (!arg) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_VAR_ID_2_ARGS(var_id, arg1, arg2) \
+    if (!delegate_) return E_FAIL; \
+    if (!IsValidId(var_id)) return E_INVALIDARG; \
+    if (!arg1) return E_INVALIDARG; \
+    if (!arg2) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_VAR_ID_3_ARGS(var_id, arg1, arg2, arg3) \
+    if (!delegate_) return E_FAIL; \
+    if (!IsValidId(var_id)) return E_INVALIDARG; \
+    if (!arg1) return E_INVALIDARG; \
+    if (!arg2) return E_INVALIDARG; \
+    if (!arg3) return E_INVALIDARG
+#define COM_OBJECT_VALIDATE_VAR_ID_4_ARGS(var_id, arg1, arg2, arg3, arg4) \
+    if (!delegate_) return E_FAIL; \
+    if (!IsValidId(var_id)) return E_INVALIDARG; \
+    if (!arg1) return E_INVALIDARG; \
+    if (!arg2) return E_INVALIDARG; \
+    if (!arg3) return E_INVALIDARG; \
+    if (!arg4) return E_INVALIDARG
+
+namespace ui {
+
+namespace {
+
+typedef base::hash_map<LONG, AXPlatformNodeWin*> UniqueIdWinMap;
+// Map from each AXPlatformNodeWin's unique id to its instance.
+base::LazyInstance<UniqueIdWinMap> g_unique_id_win_map =
+    LAZY_INSTANCE_INITIALIZER;
+
+typedef base::hash_set<AXPlatformNodeWin*> AXPlatformNodeWinSet;
+// Set of all AXPlatformNodeWin objects that were the target of an
+// alert event.
+base::LazyInstance<AXPlatformNodeWinSet> g_alert_targets =
+    LAZY_INSTANCE_INITIALIZER;
+
+LONG GetNextNegativeUniqueIdForWinAccessibility(AXPlatformNodeWin* obj) {
+  static LONG next_unique_id = -1;
+  LONG unique_id = next_unique_id;
+  if (next_unique_id == LONG_MIN)
+    next_unique_id = -1;
+  else
+    next_unique_id--;
+
+  g_unique_id_win_map.Get().insert(std::make_pair(unique_id, obj));
+
+  return unique_id;
+}
+
+void UnregisterNegativeUniqueId(LONG unique_id) {
+  g_unique_id_win_map.Get().erase(unique_id);
+}
+
+}  // namespace
+
+// static
+AXPlatformNode* AXPlatformNode::Create(AXPlatformNodeDelegate* delegate) {
+  // Make sure ATL is initialized in this module.
+  ui::win::CreateATLModuleIfNeeded();
+
+  CComObject<AXPlatformNodeWin>* instance = nullptr;
+  HRESULT hr = CComObject<AXPlatformNodeWin>::CreateInstance(&instance);
+  DCHECK(SUCCEEDED(hr));
+  instance->Init(delegate);
+  instance->AddRef();
+  return instance;
+}
+
+// static
+AXPlatformNode* AXPlatformNode::FromNativeViewAccessible(
+    gfx::NativeViewAccessible accessible) {
+  base::win::ScopedComPtr<AXPlatformNodeWin> ax_platform_node;
+  accessible->QueryInterface(ax_platform_node.Receive());
+  return ax_platform_node.get();
+}
+
+AXPlatformNodeWin::AXPlatformNodeWin()
+    : unique_id_win_(GetNextNegativeUniqueIdForWinAccessibility(this)) {
+}
+
+AXPlatformNodeWin::~AXPlatformNodeWin() {
+  CHECK(!delegate_);
+}
+
+//
+// AXPlatformNode implementation.
+//
+
+void AXPlatformNodeWin::Destroy() {
+  delegate_ = nullptr;
+  UnregisterNegativeUniqueId(unique_id_win_);
+  RemoveAlertTarget();
+  Release();
+}
+
+gfx::NativeViewAccessible AXPlatformNodeWin::GetNativeViewAccessible() {
+  return this;
+}
+
+void AXPlatformNodeWin::NotifyAccessibilityEvent(ui::AXEvent event_type) {
+  HWND hwnd = delegate_->GetTargetForNativeAccessibilityEvent();
+  if (!hwnd)
+    return;
+
+  int native_event = MSAAEvent(event_type);
+  if (native_event < EVENT_MIN)
+    return;
+
+  ::NotifyWinEvent(native_event, hwnd, OBJID_CLIENT, unique_id_win_);
+
+  // Keep track of objects that are a target of an alert event.
+  if (event_type == ui::AX_EVENT_ALERT)
+    AddAlertTarget();
+}
+
+//
+// IAccessible implementation.
+//
+
+STDMETHODIMP AXPlatformNodeWin::accHitTest(
+    LONG x_left, LONG y_top, VARIANT* child) {
+  COM_OBJECT_VALIDATE_1_ARG(child);
+  gfx::NativeViewAccessible hit_child = delegate_->HitTestSync(x_left, y_top);
+  if (!hit_child) {
+    child->vt = VT_EMPTY;
+    return S_FALSE;
+  }
+
+  if (hit_child == this) {
+    // This object is the best match, so return CHILDID_SELF. It's tempting to
+    // simplify the logic and use VT_DISPATCH everywhere, but the Windows
+    // call AccessibleObjectFromPoint will keep calling accHitTest until some
+    // object returns CHILDID_SELF.
+    child->vt = VT_I4;
+    child->lVal = CHILDID_SELF;
+    return S_OK;
+  }
+
+  // Call accHitTest recursively on the result, which may be a recursive call
+  // to this function or it may be overridden, for example in the case of a
+  // WebView.
+  HRESULT result = hit_child->accHitTest(x_left, y_top, child);
+
+  // If the recursive call returned CHILDID_SELF, we have to convert that
+  // into a VT_DISPATCH for the return value to this call.
+  if (S_OK == result && child->vt == VT_I4 && child->lVal == CHILDID_SELF) {
+    child->vt = VT_DISPATCH;
+    child->pdispVal = hit_child;
+    // Always increment ref when returning a reference to a COM object.
+    child->pdispVal->AddRef();
+  }
+  return result;
+}
+
+HRESULT AXPlatformNodeWin::accDoDefaultAction(VARIANT var_id) {
+  COM_OBJECT_VALIDATE_VAR_ID(var_id);
+  delegate_->DoDefaultAction();
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::accLocation(
+    LONG* x_left, LONG* y_top, LONG* width, LONG* height, VARIANT var_id) {
+  COM_OBJECT_VALIDATE_VAR_ID_4_ARGS(var_id, x_left, y_top, width, height);
+  gfx::Rect bounds = GetData().location;
+  bounds += delegate_->GetGlobalCoordinateOffset();
+  *x_left = bounds.x();
+  *y_top  = bounds.y();
+  *width  = bounds.width();
+  *height = bounds.height();
+
+  if (bounds.IsEmpty())
+    return S_FALSE;
+
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::accNavigate(
+    LONG nav_dir, VARIANT start, VARIANT* end) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(start, end);
+  IAccessible* result = nullptr;
+
+  switch (nav_dir) {
+    case NAVDIR_DOWN:
+    case NAVDIR_UP:
+    case NAVDIR_LEFT:
+    case NAVDIR_RIGHT:
+      // These directions are not implemented, matching Mozilla and IE.
+      return E_NOTIMPL;
+
+    case NAVDIR_FIRSTCHILD:
+      if (delegate_->GetChildCount() > 0)
+        result = delegate_->ChildAtIndex(0);
+      break;
+
+    case NAVDIR_LASTCHILD:
+      if (delegate_->GetChildCount() > 0)
+        result = delegate_->ChildAtIndex(delegate_->GetChildCount() - 1);
+      break;
+
+    case NAVDIR_NEXT:
+      result = GetNextSibling()->GetNativeViewAccessible();
+      break;
+
+    case NAVDIR_PREVIOUS:
+      result = GetPreviousSibling()->GetNativeViewAccessible();
+      break;
+
+    default:
+      return E_INVALIDARG;
+  }
+
+  if (!result) {
+    end->vt = VT_EMPTY;
+    return S_FALSE;
+  }
+
+  end->vt = VT_DISPATCH;
+  end->pdispVal = result;
+  // Always increment ref when returning a reference to a COM object.
+  end->pdispVal->AddRef();
+
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accChild(VARIANT var_child,
+                                             IDispatch** disp_child) {
+  COM_OBJECT_VALIDATE_1_ARG(disp_child);
+  LONG child_id = V_I4(&var_child);
+  if (child_id == CHILDID_SELF) {
+    *disp_child = this;
+    (*disp_child)->AddRef();
+    return S_OK;
+  }
+
+  if (child_id >= 1 && child_id <= delegate_->GetChildCount()) {
+    // Positive child ids are a 1-based child index, used by clients
+    // that want to enumerate all immediate children.
+    *disp_child = delegate_->ChildAtIndex(child_id - 1);
+    (*disp_child)->AddRef();
+    return S_OK;
+  }
+
+  if (child_id >= 0)
+    return E_FAIL;
+
+  // Negative child ids can be used to map to any descendant.
+  UniqueIdWinMap* unique_ids = g_unique_id_win_map.Pointer();
+  auto iter = unique_ids->find(child_id);
+  if (iter != unique_ids->end()) {
+    *disp_child = iter->second;
+    (*disp_child)->AddRef();
+    return S_OK;
+  }
+
+  *disp_child = nullptr;
+  return E_FAIL;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accChildCount(LONG* child_count) {
+  COM_OBJECT_VALIDATE_1_ARG(child_count);
+  *child_count = delegate_->GetChildCount();
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accDefaultAction(
+    VARIANT var_id, BSTR* def_action) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, def_action);
+  return GetStringAttributeAsBstr(ui::AX_ATTR_ACTION, def_action);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accDescription(
+    VARIANT var_id, BSTR* desc) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, desc);
+  return GetStringAttributeAsBstr(ui::AX_ATTR_DESCRIPTION, desc);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accFocus(VARIANT* focus_child) {
+  COM_OBJECT_VALIDATE_1_ARG(focus_child);
+  gfx::NativeViewAccessible focus_accessible = delegate_->GetFocus();
+  if (focus_accessible == this) {
+    focus_child->vt = VT_I4;
+    focus_child->lVal = CHILDID_SELF;
+  } else if (focus_accessible) {
+    focus_child->vt = VT_DISPATCH;
+    focus_child->pdispVal = focus_accessible;
+    focus_child->pdispVal->AddRef();
+    return S_OK;
+  } else {
+    focus_child->vt = VT_EMPTY;
+  }
+
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accKeyboardShortcut(
+    VARIANT var_id, BSTR* acc_key) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, acc_key);
+  return GetStringAttributeAsBstr(ui::AX_ATTR_SHORTCUT, acc_key);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accName(
+    VARIANT var_id, BSTR* name) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, name);
+  return GetStringAttributeAsBstr(ui::AX_ATTR_NAME, name);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accParent(
+    IDispatch** disp_parent) {
+  COM_OBJECT_VALIDATE_1_ARG(disp_parent);
+  *disp_parent = GetParent();
+  if (*disp_parent) {
+    (*disp_parent)->AddRef();
+    return S_OK;
+  }
+
+  return S_FALSE;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accRole(
+    VARIANT var_id, VARIANT* role) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, role);
+  role->vt = VT_I4;
+  role->lVal = MSAARole();
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accState(
+    VARIANT var_id, VARIANT* state) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, state);
+  state->vt = VT_I4;
+  state->lVal = MSAAState();
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accHelp(
+    VARIANT var_id, BSTR* help) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, help);
+  return GetStringAttributeAsBstr(ui::AX_ATTR_HELP, help);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accValue(VARIANT var_id, BSTR* value) {
+  COM_OBJECT_VALIDATE_VAR_ID_1_ARG(var_id, value);
+  return GetStringAttributeAsBstr(ui::AX_ATTR_VALUE, value);
+}
+
+STDMETHODIMP AXPlatformNodeWin::put_accValue(VARIANT var_id,
+                                             BSTR new_value) {
+  COM_OBJECT_VALIDATE_VAR_ID(var_id);
+  if (delegate_->SetStringValue(new_value))
+    return S_OK;
+  return E_FAIL;
+}
+
+// IAccessible functions not supported.
+
+STDMETHODIMP AXPlatformNodeWin::get_accSelection(VARIANT* selected) {
+  COM_OBJECT_VALIDATE_1_ARG(selected);
+  if (selected)
+    selected->vt = VT_EMPTY;
+  return E_NOTIMPL;
+}
+
+STDMETHODIMP AXPlatformNodeWin::accSelect(
+    LONG flagsSelect, VARIANT var_id) {
+  COM_OBJECT_VALIDATE_VAR_ID(var_id);
+  return E_NOTIMPL;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_accHelpTopic(
+    BSTR* help_file, VARIANT var_id, LONG* topic_id) {
+  COM_OBJECT_VALIDATE_VAR_ID_2_ARGS(var_id, help_file, topic_id);
+  if (help_file) {
+    *help_file = nullptr;
+  }
+  if (topic_id) {
+    *topic_id = static_cast<LONG>(-1);
+  }
+  return E_NOTIMPL;
+}
+
+STDMETHODIMP AXPlatformNodeWin::put_accName(
+    VARIANT var_id, BSTR put_name) {
+  COM_OBJECT_VALIDATE_VAR_ID(var_id);
+  // Deprecated.
+  return E_NOTIMPL;
+}
+
+//
+// IAccessible2 implementation.
+//
+
+STDMETHODIMP AXPlatformNodeWin::role(LONG* role) {
+  COM_OBJECT_VALIDATE_1_ARG(role);
+  *role = MSAARole();
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_states(AccessibleStates* states) {
+  COM_OBJECT_VALIDATE_1_ARG(states);
+  // There are only a couple of states we need to support
+  // in IAccessible2. If any more are added, we may want to
+  // add a helper function like MSAAState.
+  *states = IA2_STATE_OPAQUE;
+  if (GetData().state & (1 << ui::AX_STATE_EDITABLE))
+    *states |= IA2_STATE_EDITABLE;
+
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_uniqueID(LONG* unique_id) {
+  COM_OBJECT_VALIDATE_1_ARG(unique_id);
+  *unique_id = unique_id_win_;
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_windowHandle(HWND* window_handle) {
+  COM_OBJECT_VALIDATE_1_ARG(window_handle);
+  *window_handle = delegate_->GetTargetForNativeAccessibilityEvent();
+  return *window_handle ? S_OK : S_FALSE;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_relationTargetsOfType(
+    BSTR type_bstr,
+    long max_targets,
+    IUnknown ***targets,
+    long *n_targets) {
+  COM_OBJECT_VALIDATE_2_ARGS(targets, n_targets);
+
+  *n_targets = 0;
+  *targets = nullptr;
+
+  // Only respond to requests for relations of type "alerts".
+  base::string16 type(type_bstr);
+  if (type != L"alerts")
+    return S_FALSE;
+
+  // Collect all of the objects that have had an alert fired on them that
+  // are a descendant of this object.
+  std::vector<AXPlatformNodeWin*> alert_targets;
+  for (auto iter = g_alert_targets.Get().begin();
+       iter != g_alert_targets.Get().end();
+       ++iter) {
+    AXPlatformNodeWin* target = *iter;
+    if (IsDescendant(target))
+      alert_targets.push_back(target);
+  }
+
+  long count = static_cast<long>(alert_targets.size());
+  if (count == 0)
+    return S_FALSE;
+
+  // Don't return more targets than max_targets - but note that the caller
+  // is allowed to specify max_targets=0 to mean no limit.
+  if (max_targets > 0 && count > max_targets)
+    count = max_targets;
+
+  // Return the number of targets.
+  *n_targets = count;
+
+  // Allocate COM memory for the result array and populate it.
+  *targets = static_cast<IUnknown**>(
+      CoTaskMemAlloc(count * sizeof(IUnknown*)));
+  for (long i = 0; i < count; ++i) {
+    (*targets)[i] = static_cast<IAccessible*>(alert_targets[i]);
+    (*targets)[i]->AddRef();
+  }
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_attributes(BSTR* attributes) {
+  COM_OBJECT_VALIDATE_1_ARG(attributes);
+  base::string16 attributes_str;
+
+  // Text fields need to report the attribute "text-model:a1" to instruct
+  // screen readers to use IAccessible2 APIs to handle text editing in this
+  // object (as opposed to treating it like a native Windows text box).
+  // The text-model:a1 attribute is documented here:
+  // http://www.linuxfoundation.org/collaborate/workgroups/accessibility/ia2/ia2_implementation_guide
+  if (GetData().role == ui::AX_ROLE_TEXT_FIELD) {
+    attributes_str = L"text-model:a1;";
+  }
+
+  *attributes = SysAllocString(attributes_str.c_str());
+  DCHECK(*attributes);
+  return S_OK;
+}
+
+//
+// IAccessibleText
+//
+
+STDMETHODIMP AXPlatformNodeWin::get_nCharacters(LONG* n_characters) {
+  COM_OBJECT_VALIDATE_1_ARG(n_characters);
+  base::string16 text = TextForIAccessibleText();
+  *n_characters = static_cast<LONG>(text.size());
+
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_caretOffset(LONG* offset) {
+  COM_OBJECT_VALIDATE_1_ARG(offset);
+  *offset = static_cast<LONG>(GetIntAttribute(ui::AX_ATTR_TEXT_SEL_END));
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_nSelections(LONG* n_selections) {
+  COM_OBJECT_VALIDATE_1_ARG(n_selections);
+  int sel_start = GetIntAttribute(ui::AX_ATTR_TEXT_SEL_START);
+  int sel_end = GetIntAttribute(ui::AX_ATTR_TEXT_SEL_END);
+  if (sel_start != sel_end)
+    *n_selections = 1;
+  else
+    *n_selections = 0;
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_selection(LONG selection_index,
+                                              LONG* start_offset,
+                                              LONG* end_offset) {
+  COM_OBJECT_VALIDATE_2_ARGS(start_offset, end_offset);
+  if (selection_index != 0)
+    return E_INVALIDARG;
+
+  *start_offset = static_cast<LONG>(
+      GetIntAttribute(ui::AX_ATTR_TEXT_SEL_START));
+  *end_offset = static_cast<LONG>(
+      GetIntAttribute(ui::AX_ATTR_TEXT_SEL_END));
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_text(LONG start_offset,
+                                         LONG end_offset,
+                                         BSTR* text) {
+  COM_OBJECT_VALIDATE_1_ARG(text);
+  int sel_end = GetIntAttribute(ui::AX_ATTR_TEXT_SEL_START);
+  base::string16 text_str = TextForIAccessibleText();
+  LONG len = static_cast<LONG>(text_str.size());
+
+  if (start_offset == IA2_TEXT_OFFSET_LENGTH) {
+    start_offset = len;
+  } else if (start_offset == IA2_TEXT_OFFSET_CARET) {
+    start_offset = static_cast<LONG>(sel_end);
+  }
+  if (end_offset == IA2_TEXT_OFFSET_LENGTH) {
+    end_offset = static_cast<LONG>(text_str.size());
+  } else if (end_offset == IA2_TEXT_OFFSET_CARET) {
+    end_offset = static_cast<LONG>(sel_end);
+  }
+
+  // The spec allows the arguments to be reversed.
+  if (start_offset > end_offset) {
+    LONG tmp = start_offset;
+    start_offset = end_offset;
+    end_offset = tmp;
+  }
+
+  // The spec does not allow the start or end offsets to be out or range;
+  // we must return an error if so.
+  if (start_offset < 0)
+    return E_INVALIDARG;
+  if (end_offset > len)
+    return E_INVALIDARG;
+
+  base::string16 substr =
+      text_str.substr(start_offset, end_offset - start_offset);
+  if (substr.empty())
+    return S_FALSE;
+
+  *text = SysAllocString(substr.c_str());
+  DCHECK(*text);
+  return S_OK;
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_textAtOffset(
+    LONG offset,
+    enum IA2TextBoundaryType boundary_type,
+    LONG* start_offset, LONG* end_offset,
+    BSTR* text) {
+  COM_OBJECT_VALIDATE_3_ARGS(start_offset, end_offset, text);
+  // The IAccessible2 spec says we don't have to implement the "sentence"
+  // boundary type, we can just let the screen reader handle it.
+  if (boundary_type == IA2_TEXT_BOUNDARY_SENTENCE) {
+    *start_offset = 0;
+    *end_offset = 0;
+    *text = nullptr;
+    return S_FALSE;
+  }
+
+  const base::string16& text_str = TextForIAccessibleText();
+
+  *start_offset = FindBoundary(
+      text_str, boundary_type, offset, ui::BACKWARDS_DIRECTION);
+  *end_offset = FindBoundary(
+      text_str, boundary_type, offset, ui::FORWARDS_DIRECTION);
+  return get_text(*start_offset, *end_offset, text);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_textBeforeOffset(
+    LONG offset,
+    enum IA2TextBoundaryType boundary_type,
+    LONG* start_offset, LONG* end_offset,
+    BSTR* text) {
+  if (!start_offset || !end_offset || !text)
+    return E_INVALIDARG;
+
+  // The IAccessible2 spec says we don't have to implement the "sentence"
+  // boundary type, we can just let the screenreader handle it.
+  if (boundary_type == IA2_TEXT_BOUNDARY_SENTENCE) {
+    *start_offset = 0;
+    *end_offset = 0;
+    *text = nullptr;
+    return S_FALSE;
+  }
+
+  const base::string16& text_str = TextForIAccessibleText();
+
+  *start_offset = FindBoundary(
+      text_str, boundary_type, offset, ui::BACKWARDS_DIRECTION);
+  *end_offset = offset;
+  return get_text(*start_offset, *end_offset, text);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_textAfterOffset(
+    LONG offset,
+    enum IA2TextBoundaryType boundary_type,
+    LONG* start_offset, LONG* end_offset,
+    BSTR* text) {
+  if (!start_offset || !end_offset || !text)
+    return E_INVALIDARG;
+
+  // The IAccessible2 spec says we don't have to implement the "sentence"
+  // boundary type, we can just let the screenreader handle it.
+  if (boundary_type == IA2_TEXT_BOUNDARY_SENTENCE) {
+    *start_offset = 0;
+    *end_offset = 0;
+    *text = nullptr;
+    return S_FALSE;
+  }
+
+  const base::string16& text_str = TextForIAccessibleText();
+
+  *start_offset = offset;
+  *end_offset = FindBoundary(
+      text_str, boundary_type, offset, ui::FORWARDS_DIRECTION);
+  return get_text(*start_offset, *end_offset, text);
+}
+
+STDMETHODIMP AXPlatformNodeWin::get_offsetAtPoint(
+    LONG x, LONG y, enum IA2CoordinateType coord_type, LONG* offset) {
+  COM_OBJECT_VALIDATE_1_ARG(offset);
+  // We don't support this method, but we have to return something
+  // rather than E_NOTIMPL or screen readers will complain.
+  *offset = 0;
+  return S_OK;
+}
+
+//
+// IServiceProvider implementation.
+//
+
+STDMETHODIMP AXPlatformNodeWin::QueryService(
+    REFGUID guidService, REFIID riid, void** object) {
+  COM_OBJECT_VALIDATE_1_ARG(object);
+  if (guidService == IID_IAccessible ||
+      guidService == IID_IAccessible2 ||
+      guidService == IID_IAccessible2_2 ||
+      guidService == IID_IAccessibleText) {
+    return QueryInterface(riid, object);
+  }
+
+  *object = nullptr;
+  return E_FAIL;
+}
+
+//
+// Private member functions.
+//
+
+bool AXPlatformNodeWin::IsValidId(const VARIANT& child) const {
+  // Since we have a separate IAccessible COM object for each node, we only
+  // support the CHILDID_SELF id.
+  return (VT_I4 == child.vt) && (CHILDID_SELF == child.lVal);
+}
+
+int AXPlatformNodeWin::MSAARole() {
+  switch (GetData().role) {
+    case ui::AX_ROLE_ALERT:
+      return ROLE_SYSTEM_ALERT;
+    case ui::AX_ROLE_APPLICATION:
+      return ROLE_SYSTEM_APPLICATION;
+    case ui::AX_ROLE_BUTTON_DROP_DOWN:
+      return ROLE_SYSTEM_BUTTONDROPDOWN;
+    case ui::AX_ROLE_POP_UP_BUTTON:
+      return ROLE_SYSTEM_BUTTONMENU;
+    case ui::AX_ROLE_CHECK_BOX:
+      return ROLE_SYSTEM_CHECKBUTTON;
+    case ui::AX_ROLE_COMBO_BOX:
+      return ROLE_SYSTEM_COMBOBOX;
+    case ui::AX_ROLE_DIALOG:
+      return ROLE_SYSTEM_DIALOG;
+    case ui::AX_ROLE_GROUP:
+      return ROLE_SYSTEM_GROUPING;
+    case ui::AX_ROLE_IMAGE:
+      return ROLE_SYSTEM_GRAPHIC;
+    case ui::AX_ROLE_LINK:
+      return ROLE_SYSTEM_LINK;
+    case ui::AX_ROLE_LOCATION_BAR:
+      return ROLE_SYSTEM_GROUPING;
+    case ui::AX_ROLE_MENU_BAR:
+      return ROLE_SYSTEM_MENUBAR;
+    case ui::AX_ROLE_MENU_ITEM:
+      return ROLE_SYSTEM_MENUITEM;
+    case ui::AX_ROLE_MENU_LIST_POPUP:
+      return ROLE_SYSTEM_MENUPOPUP;
+    case ui::AX_ROLE_TREE:
+      return ROLE_SYSTEM_OUTLINE;
+    case ui::AX_ROLE_TREE_ITEM:
+      return ROLE_SYSTEM_OUTLINEITEM;
+    case ui::AX_ROLE_TAB:
+      return ROLE_SYSTEM_PAGETAB;
+    case ui::AX_ROLE_TAB_LIST:
+      return ROLE_SYSTEM_PAGETABLIST;
+    case ui::AX_ROLE_PANE:
+      return ROLE_SYSTEM_PANE;
+    case ui::AX_ROLE_PROGRESS_INDICATOR:
+      return ROLE_SYSTEM_PROGRESSBAR;
+    case ui::AX_ROLE_BUTTON:
+      return ROLE_SYSTEM_PUSHBUTTON;
+    case ui::AX_ROLE_RADIO_BUTTON:
+      return ROLE_SYSTEM_RADIOBUTTON;
+    case ui::AX_ROLE_SCROLL_BAR:
+      return ROLE_SYSTEM_SCROLLBAR;
+    case ui::AX_ROLE_SPLITTER:
+      return ROLE_SYSTEM_SEPARATOR;
+    case ui::AX_ROLE_SLIDER:
+      return ROLE_SYSTEM_SLIDER;
+    case ui::AX_ROLE_STATIC_TEXT:
+      return ROLE_SYSTEM_STATICTEXT;
+    case ui::AX_ROLE_TEXT_FIELD:
+      return ROLE_SYSTEM_TEXT;
+    case ui::AX_ROLE_TITLE_BAR:
+      return ROLE_SYSTEM_TITLEBAR;
+    case ui::AX_ROLE_TOOLBAR:
+      return ROLE_SYSTEM_TOOLBAR;
+    case ui::AX_ROLE_WEB_VIEW:
+      return ROLE_SYSTEM_GROUPING;
+    case ui::AX_ROLE_WINDOW:
+      return ROLE_SYSTEM_WINDOW;
+    case ui::AX_ROLE_CLIENT:
+    default:
+      // This is the default role for MSAA.
+      return ROLE_SYSTEM_CLIENT;
+  }
+}
+
+int AXPlatformNodeWin::MSAAState() {
+  uint32 state = GetData().state;
+
+  int msaa_state = 0;
+  if (state & (1 << ui::AX_STATE_CHECKED))
+    msaa_state |= STATE_SYSTEM_CHECKED;
+  if (state & (1 << ui::AX_STATE_COLLAPSED))
+    msaa_state |= STATE_SYSTEM_COLLAPSED;
+  if (state & (1 << ui::AX_STATE_DEFAULT))
+    msaa_state |= STATE_SYSTEM_DEFAULT;
+  if (state & (1 << ui::AX_STATE_EXPANDED))
+    msaa_state |= STATE_SYSTEM_EXPANDED;
+  if (state & (1 << ui::AX_STATE_FOCUSABLE))
+    msaa_state |= STATE_SYSTEM_FOCUSABLE;
+  if (state & (1 << ui::AX_STATE_FOCUSED))
+    msaa_state |= STATE_SYSTEM_FOCUSED;
+  if (state & (1 << ui::AX_STATE_HASPOPUP))
+    msaa_state |= STATE_SYSTEM_HASPOPUP;
+  if (state & (1 << ui::AX_STATE_HOVERED))
+    msaa_state |= STATE_SYSTEM_HOTTRACKED;
+  if (state & (1 << ui::AX_STATE_INVISIBLE))
+    msaa_state |= STATE_SYSTEM_INVISIBLE;
+  if (state & (1 << ui::AX_STATE_LINKED))
+    msaa_state |= STATE_SYSTEM_LINKED;
+  if (state & (1 << ui::AX_STATE_OFFSCREEN))
+    msaa_state |= STATE_SYSTEM_OFFSCREEN;
+  if (state & (1 << ui::AX_STATE_PRESSED))
+    msaa_state |= STATE_SYSTEM_PRESSED;
+  if (state & (1 << ui::AX_STATE_PROTECTED))
+    msaa_state |= STATE_SYSTEM_PROTECTED;
+  if (state & (1 << ui::AX_STATE_READ_ONLY))
+    msaa_state |= STATE_SYSTEM_READONLY;
+  if (state & (1 << ui::AX_STATE_SELECTABLE))
+    msaa_state |= STATE_SYSTEM_SELECTABLE;
+  if (state & (1 << ui::AX_STATE_SELECTED))
+    msaa_state |= STATE_SYSTEM_SELECTED;
+  if (state & (1 << ui::AX_STATE_DISABLED))
+    msaa_state |= STATE_SYSTEM_UNAVAILABLE;
+
+  return msaa_state;
+}
+
+int AXPlatformNodeWin::MSAAEvent(ui::AXEvent event) {
+  switch (event) {
+    case ui::AX_EVENT_ALERT:
+      return EVENT_SYSTEM_ALERT;
+    case ui::AX_EVENT_FOCUS:
+      return EVENT_OBJECT_FOCUS;
+    case ui::AX_EVENT_MENU_START:
+      return EVENT_SYSTEM_MENUSTART;
+    case ui::AX_EVENT_MENU_END:
+      return EVENT_SYSTEM_MENUEND;
+    case ui::AX_EVENT_MENU_POPUP_START:
+      return EVENT_SYSTEM_MENUPOPUPSTART;
+    case ui::AX_EVENT_MENU_POPUP_END:
+      return EVENT_SYSTEM_MENUPOPUPEND;
+    case ui::AX_EVENT_SELECTION:
+      return EVENT_OBJECT_SELECTION;
+    case ui::AX_EVENT_SELECTION_ADD:
+      return EVENT_OBJECT_SELECTIONADD;
+    case ui::AX_EVENT_SELECTION_REMOVE:
+      return EVENT_OBJECT_SELECTIONREMOVE;
+    case ui::AX_EVENT_TEXT_CHANGED:
+      return EVENT_OBJECT_NAMECHANGE;
+    case ui::AX_EVENT_TEXT_SELECTION_CHANGED:
+      return IA2_EVENT_TEXT_CARET_MOVED;
+    case ui::AX_EVENT_VALUE_CHANGED:
+      return EVENT_OBJECT_VALUECHANGE;
+    default:
+      return -1;
+  }
+}
+
+HRESULT AXPlatformNodeWin::GetStringAttributeAsBstr(
+    ui::AXStringAttribute attribute,
+    BSTR* value_bstr) const {
+  base::string16 str;
+
+  if (!GetString16Attribute(attribute, &str))
+    return S_FALSE;
+
+  if (str.empty())
+    return S_FALSE;
+
+  *value_bstr = SysAllocString(str.c_str());
+  DCHECK(*value_bstr);
+
+  return S_OK;
+}
+
+void AXPlatformNodeWin::AddAlertTarget() {
+  g_alert_targets.Get().insert(this);
+}
+
+void AXPlatformNodeWin::RemoveAlertTarget() {
+  if (g_alert_targets.Get().find(this) != g_alert_targets.Get().end())
+    g_alert_targets.Get().erase(this);
+}
+
+base::string16 AXPlatformNodeWin::TextForIAccessibleText() {
+  if (GetData().role == ui::AX_ROLE_TEXT_FIELD)
+    return GetString16Attribute(ui::AX_ATTR_VALUE);
+  else
+    return GetString16Attribute(ui::AX_ATTR_NAME);
+}
+
+void AXPlatformNodeWin::HandleSpecialTextOffset(
+    const base::string16& text, LONG* offset) {
+  if (*offset == IA2_TEXT_OFFSET_LENGTH) {
+    *offset = static_cast<LONG>(text.size());
+  } else if (*offset == IA2_TEXT_OFFSET_CARET) {
+    get_caretOffset(offset);
+  }
+}
+
+ui::TextBoundaryType AXPlatformNodeWin::IA2TextBoundaryToTextBoundary(
+    IA2TextBoundaryType ia2_boundary) {
+  switch(ia2_boundary) {
+    case IA2_TEXT_BOUNDARY_CHAR: return ui::CHAR_BOUNDARY;
+    case IA2_TEXT_BOUNDARY_WORD: return ui::WORD_BOUNDARY;
+    case IA2_TEXT_BOUNDARY_LINE: return ui::LINE_BOUNDARY;
+    case IA2_TEXT_BOUNDARY_SENTENCE: return ui::SENTENCE_BOUNDARY;
+    case IA2_TEXT_BOUNDARY_PARAGRAPH: return ui::PARAGRAPH_BOUNDARY;
+    case IA2_TEXT_BOUNDARY_ALL: return ui::ALL_BOUNDARY;
+    default:
+      NOTREACHED();
+      return ui::CHAR_BOUNDARY;
+  }
+}
+
+LONG AXPlatformNodeWin::FindBoundary(
+    const base::string16& text,
+    IA2TextBoundaryType ia2_boundary,
+    LONG start_offset,
+    ui::TextBoundaryDirection direction) {
+  HandleSpecialTextOffset(text, &start_offset);
+  ui::TextBoundaryType boundary = IA2TextBoundaryToTextBoundary(ia2_boundary);
+  std::vector<int32> line_breaks;
+  return ui::FindAccessibleTextBoundary(
+      text, line_breaks, boundary, start_offset, direction);
+}
+
+}  // namespace ui