Implement initial support for nesting one ax tree in another.

content/browser/accessibility/frame_tree_accessibility.h

Index: content/browser/accessibility/frame_tree_accessibility.h
diff --git a/content/browser/accessibility/frame_tree_accessibility.h b/content/browser/accessibility/frame_tree_accessibility.h
new file mode 100644
index 0000000000000000000000000000000000000000..a30e0569b090c4d0e37b11a34682f021713f2cc1
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+++ b/content/browser/accessibility/frame_tree_accessibility.h
@@ -0,0 +1,81 @@
+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_ACCESSIBILITY_FRAME_TREE_ACCESSIBILITY_H_
+#define CONTENT_BROWSER_ACCESSIBILITY_FRAME_TREE_ACCESSIBILITY_H_
+
+#include "base/basictypes.h"
+#include "base/containers/hash_tables.h"
+#include "base/memory/singleton.h"
+#include "content/browser/accessibility/browser_accessibility_manager.h"
+#include "content/common/content_export.h"
+
+#if defined(COMPILER_GCC)
+namespace BASE_HASH_NAMESPACE {
+
+template<>
+struct hash<content::BrowserAccessibilityDelegate*> {
+  std::size_t operator()(content::BrowserAccessibilityDelegate* const& ptr)
+      const {
+    return hash<size_t>()(reinterpret_cast<size_t>(ptr));
+  }
+};
+
+}  // namespace __gnu_cxx
+
+#elif defined(COMPILER_MSVC)
+namespace stdext {
+
+template<>
+inline size_t hash_value(content::BrowserAccessibilityDelegate* const& ptr) {
+  return hash_value(reinterpret_cast<size_t>(ptr));
+}
+
+}  // namespace stdext
+
+#endif // COMPILER
+
+namespace content {
+
+// This singleton manages relationships between accessibility trees that are
+// nested in other accessibility trees, due to a <webview> element or
+// an out-of-process iframe. Every accessible frame is identified by its
+// host BrowserAccessibilityDelegate and given a unique id.
+class CONTENT_EXPORT FrameTreeAccessibility {
+ public:
+  // Get the single instance of this class.
+  static FrameTreeAccessibility* GetInstance();
+
+  // The class that implements BrowserAccessibilityDelegate registers each
+  // frame on creation and unregisters it on deletion, and associates a
+  // BrowserAccessibilityManager with a frame.
+  void OnFrameCreated(BrowserAccessibilityDelegate* frame);
+  void OnFrameDeleted(BrowserAccessibilityDelegate* frame);
+  void SetFrameAccessibilityManager(BrowserAccessibilityDelegate* frame,
+                                    BrowserAccessibilityManager* manager);
+
+  // When a node in an accessible tree contains a reference to an accessible
+  // frame, it can be looked up here. Note that it's not safe to hold onto a
+  // reference to a BrowserAccessibilityDelegate or BrowserAccessibilityManager
+  // because they could be subsequently deleted.
+  int32 GetFrameId(BrowserAccessibilityDelegate* frame);
+  BrowserAccessibilityDelegate* FindFrameById(int32 id);
+  BrowserAccessibilityManager* FindAccessibilityManagerById(int32 id);
+
+ protected:
+  FrameTreeAccessibility();
+  ~FrameTreeAccessibility();
+
+ private:
+  int next_id_;
+  base::hash_map<BrowserAccessibilityDelegate*, int32> frame_to_id_;
+  base::hash_map<int32, BrowserAccessibilityDelegate*> id_to_frame_;
+  base::hash_map<int32, BrowserAccessibilityManager*> id_to_manager_;
+
+  friend struct DefaultSingletonTraits<FrameTreeAccessibility>;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ACCESSIBILITY_FRAME_TREE_ACCESSIBILITY_H_