Added a class acting as a fake caret for accessibility.

content/browser/renderer_host/legacy_render_widget_host_win.cc

Index: content/browser/renderer_host/legacy_render_widget_host_win.cc
diff --git a/content/browser/renderer_host/legacy_render_widget_host_win.cc b/content/browser/renderer_host/legacy_render_widget_host_win.cc
index c619024b9d201e64a4d29ee70c5c3b9c87bf3c5c..af1d083f2fc116d90ea0c2a723765632f97d9e7c 100644
--- a/content/browser/renderer_host/legacy_render_widget_host_win.cc
+++ b/content/browser/renderer_host/legacy_render_widget_host_win.cc
@@ -4,6 +4,8 @@
 
 #include "content/browser/renderer_host/legacy_render_widget_host_win.h"
 
+#include <atlcom.h>
+
 #include <memory>
 
 #include "base/command_line.h"
@@ -15,6 +17,7 @@
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_view_aura.h"
 #include "content/public/common/content_switches.h"
+#include "ui/accessibility/platform/ax_fake_caret_win.h"
 #include "ui/base/view_prop.h"
 #include "ui/base/win/internal_constants.h"
 #include "ui/base/win/window_event_target.h"
@@ -170,24 +173,31 @@ LRESULT LegacyRenderWidgetHostHWND::OnGetObject(UINT message,
     return static_cast<LRESULT>(0L);
   }
 
-  if (static_cast<DWORD>(OBJID_CLIENT) != obj_id || !host_)
-    return static_cast<LRESULT>(0L);
-
-  RenderWidgetHostImpl* rwhi = RenderWidgetHostImpl::From(
-      host_->GetRenderWidgetHost());
-  if (!rwhi)
-    return static_cast<LRESULT>(0L);
-
-  BrowserAccessibilityManagerWin* manager =
-      static_cast<BrowserAccessibilityManagerWin*>(
-          rwhi->GetRootBrowserAccessibilityManager());
-  if (!manager)
-    return static_cast<LRESULT>(0L);
+  if (static_cast<DWORD>(OBJID_CLIENT) == obj_id && host_) {
+    RenderWidgetHostImpl* rwhi =
+        RenderWidgetHostImpl::From(host_->GetRenderWidgetHost());
+    if (!rwhi)
+      return static_cast<LRESULT>(0L);
+
+    BrowserAccessibilityManagerWin* manager =
+        static_cast<BrowserAccessibilityManagerWin*>(
+            rwhi->GetRootBrowserAccessibilityManager());
+    if (!manager)
+      return static_cast<LRESULT>(0L);
+
+    base::win::ScopedComPtr<IAccessible> root(
+        ToBrowserAccessibilityWin(manager->GetRoot()));
+    return LresultFromObject(IID_IAccessible, w_param,
+                             static_cast<IAccessible*>(root.Detach()));
+  } else if (static_cast<DWORD>(OBJID_CARET) == obj_id) {

[dougt, 2017/03/28 15:23:44]

nit:

the above if-stmt returns making the following else stmt a non-sequitur.  It
might be clearer to not use the 'else'.

+    // Used by some assistive software to retrieve the location of the caret.
+    CComObjectStack<ui::AXFakeCaretWin> fake_caret;
+    DCHECK_EQ(fake_caret.m_hResFinalConstruct, S_OK);

[dougt, 2017/03/28 15:23:44]

I am confused by this DCHECK. Are you concerned with the result of the
construction of the stack of AXFakeCaretWin's?  Or are you just not sure if you
should check it or not at this point?

+    return LresultFromObject(IID_IAccessible, w_param,
+                             static_cast<IAccessible*>(&fake_caret));
+  }
 
-  base::win::ScopedComPtr<IAccessible> root(
-      ToBrowserAccessibilityWin(manager->GetRoot()));
-  return LresultFromObject(IID_IAccessible, w_param,
-      static_cast<IAccessible*>(root.Detach()));
+  return static_cast<LRESULT>(0L);
 }
 
 // We send keyboard/mouse/touch messages to the parent window via SendMessage.