Check validity of using IA2 interface prior to using it

The ax_dump_events tool is crashing when IA2 not supported on an object.
This checks that the queryInterface succeeded and that we hold a non-null
IA2 pointer, before trying to use the IA2 pointer.

Bug: None
Change-Id: I4e2e2b469b0d891eac920fac1273436d28702f85
Reviewed-on: https://chromium-review.googlesource.com/1115561
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570541}

content/browser/accessibility/accessibility_event_recorder_win.cc

@@ -258,12 +258,13 @@ void AccessibilityEventRecorderWin::OnWinEventHook(
   AccessibleStates ia2_state = 0;
   Microsoft::WRL::ComPtr<IAccessible2> iaccessible2;
   hr = QueryIAccessible2(iaccessible.Get(), iaccessible2.GetAddressOf());
+  bool has_ia2 = SUCCEEDED(hr) && iaccessible2;
 
   base::string16 html_tag;
   base::string16 obj_class;
   base::string16 html_id;
 
-  if (SUCCEEDED(hr)) {
+  if (has_ia2) {
     iaccessible2->get_states(&ia2_state);
     base::win::ScopedBstr attributes_bstr;
     if (S_OK == iaccessible2->get_attributes(attributes_bstr.Receive())) {
@@ -309,7 +310,8 @@ void AccessibilityEventRecorderWin::OnWinEventHook(
 
   // Group position, e.g. L3, 5 of 7
   LONG group_level, similar_items_in_group, position_in_group;
-  if (iaccessible2->get_groupPosition(&group_level, &similar_items_in_group,
+  if (has_ia2 &&
+      iaccessible2->get_groupPosition(&group_level, &similar_items_in_group,
                                       &position_in_group) == S_OK) {
     if (group_level)
       log += base::StringPrintf(" level=%ld", group_level);