Revert 146726 "AXObjectCache gets recreated during document tear..."

Source/WebCore/editing/chromium/FrameSelectionChromium.cpp

Index: Source/WebCore/editing/chromium/FrameSelectionChromium.cpp
===================================================================
--- Source/WebCore/editing/chromium/FrameSelectionChromium.cpp	(revision 146890)
+++ Source/WebCore/editing/chromium/FrameSelectionChromium.cpp	(working copy)
@@ -40,9 +40,9 @@
 void FrameSelection::notifyAccessibilityForSelectionChange()
 {
     // FIXME: Support editable text in chromium.
-    if (m_selection.start().isNotNull() && m_selection.end().isNotNull()) {
-        if (AXObjectCache* cache = m_frame->document()->existingAXObjectCache())
-            cache->postNotification(m_selection.start().deprecatedNode(), AXObjectCache::AXSelectedTextChanged, false);
+    if (AXObjectCache::accessibilityEnabled() && m_selection.start().isNotNull() && m_selection.end().isNotNull()) {
+        Document* document = m_frame->document();
+        document->axObjectCache()->postNotification(m_selection.start().deprecatedNode(), AXObjectCache::AXSelectedTextChanged, false);
     }
 }