Implement BrowserAccessibility accNavigate() in terms of 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 <limits.h>
 #include <oleacc.h>
 #include <stdint.h>
 
@@ skipping 262 matching lines @@
     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;
 
+  if ((nav_dir == NAVDIR_LASTCHILD || nav_dir == NAVDIR_FIRSTCHILD) &&
+      start.lVal != CHILDID_SELF) {
+    // MSAA states that navigating to first/last child can only be from self.
+    return E_INVALIDARG;
+  }
+
   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)
@@ skipping 901 matching lines @@
     ui::TextBoundaryDirection direction) {
   HandleSpecialTextOffset(&start_offset);
   ui::TextBoundaryType boundary = IA2TextBoundaryToTextBoundary(ia2_boundary);
   std::vector<int32_t> line_breaks;
   return static_cast<LONG>(ui::FindAccessibleTextBoundary(
       text, line_breaks, boundary, start_offset, direction,
       AX_TEXT_AFFINITY_DOWNSTREAM));
 }
 
 }  // namespace ui