Adds MSAA/IAccessible exposure of web content.

chrome/browser/render_widget_host_hwnd.h

Index: chrome/browser/render_widget_host_hwnd.h
===================================================================
--- chrome/browser/render_widget_host_hwnd.h	(revision 2530)
+++ chrome/browser/render_widget_host_hwnd.h	(working copy)
@@ -107,6 +107,7 @@
     MESSAGE_HANDLER(WM_SYSCHAR, OnKeyEvent)
     MESSAGE_HANDLER(WM_IME_CHAR, OnKeyEvent)
     MESSAGE_HANDLER(WM_MOUSEACTIVATE, OnMouseActivate)
+    MESSAGE_HANDLER(WM_GETOBJECT, OnGetObject)
   END_MSG_MAP()
 
   // Overridden from RenderWidgetHostView:
@@ -164,6 +165,9 @@
   LRESULT OnWheelEvent(
       UINT message, WPARAM wparam, LPARAM lparam, BOOL& handled);
   LRESULT OnMouseActivate(UINT, WPARAM, LPARAM, BOOL& handled);
+  // Handle MSAA requests for accessibility information.
+  LRESULT OnGetObject(UINT message, WPARAM wparam, LPARAM lparam,
+                      BOOL& handled);
   // Handle vertical scrolling
   LRESULT OnVScroll(int code, short position, HWND scrollbar_control);
   // Handle horizontal scrolling
@@ -246,6 +250,10 @@
   // when shown again.
   HWND parent_hwnd_;
 
+  // Instance of accessibility information for the root of the MSAA
+  // tree representation of the WebKit render tree.
+  CComPtr<IAccessible> browser_accessibility_root_;
+
   // The time at which this view started displaying white pixels as a result of
   // not having anything to paint (empty backing store from renderer). This
   // value returns true for is_null() if we are not recording whiteout times.