Add WebScopedAXContext to allow a one-time snapshot of accessibility.

public/web/WebAXObject.h

Index: public/web/WebAXObject.h
diff --git a/public/web/WebAXObject.h b/public/web/WebAXObject.h
index 12c4c12e0fa5a2825d45c4ed8d88f18b6ddd01fe..c68c0e4a571f5664031803b32bb2166c6b2fa1b3 100644
--- a/public/web/WebAXObject.h
+++ b/public/web/WebAXObject.h
@@ -43,6 +43,8 @@ namespace WTF { template <typename T> class PassRefPtr; }
 namespace blink {
 
 class AXObject;
+class ScopedAXObjectCache;
+class WebAXObject;
 class WebNode;
 class WebDocument;
 class WebString;
@@ -50,6 +52,20 @@ class WebURL;
 struct WebPoint;
 struct WebRect;
 
+// An instance of this class, while kept alive, indicates that accessibility
+// should be temporarily enabled. If accessibility was enabled globally
+// (WebSettings::setAccessibilityEnabled), this will have no effect.
+class WebScopedAXContext {
+public:
+    BLINK_EXPORT WebScopedAXContext(WebDocument& rootDocument);
+    BLINK_EXPORT ~WebScopedAXContext();
+
+    BLINK_EXPORT WebAXObject root() const;
+
+private:
+    WebPrivatePtr<ScopedAXObjectCache> m_private;
+};
+
 // A container for passing around a reference to AXObject.
 class WebAXObject {
 public: