Create Source/modules/accessibility/ and move most of core/accessibility/* into it

Source/core/accessibility/AXObjectCache.h

Index: Source/core/accessibility/AXObjectCache.h
diff --git a/Source/core/accessibility/AXObjectCache.h b/Source/core/accessibility/AXObjectCache.h
index 47ce197848ee747b83152ae97f7ee5e3017892f5..6b7d2c133058c6388382bf1de18879f61505e86a 100644
--- a/Source/core/accessibility/AXObjectCache.h
+++ b/Source/core/accessibility/AXObjectCache.h
@@ -26,11 +26,12 @@
 #ifndef AXObjectCache_h
 #define AXObjectCache_h
 
-#include "core/accessibility/AXObject.h"
 #include "core/dom/Document.h"
 
-namespace blink {
+typedef unsigned AXID;
 
+namespace blink {
+class AXObject;
 class AbstractInlineTextBox;
 class FrameView;
 class Page;