Add support for retrieving image thumbnails as part of the accessibility tree.

content/renderer/accessibility/blink_ax_tree_source.h

Index: content/renderer/accessibility/blink_ax_tree_source.h
diff --git a/content/renderer/accessibility/blink_ax_tree_source.h b/content/renderer/accessibility/blink_ax_tree_source.h
index 2f4001c558015deef532eb487f86d43037451c0c..aecc61ffcc429c66666ff14d499c843edb4a6993 100644
--- a/content/renderer/accessibility/blink_ax_tree_source.h
+++ b/content/renderer/accessibility/blink_ax_tree_source.h
@@ -54,6 +54,18 @@ class BlinkAXTreeSource
   // Walks up the ancestor chain to see if this is a descendant of the root.
   bool IsInTree(blink::WebAXObject node) const;
 
+  // Set the id of the node to fetch image data for. Normally the content
+  // of images is not part of the accessibility tree, but one node at a
+  // time can be designated as the image data node, which will send the
+  // contents of the image with each accessibility update until another
+  // node is designated.
+  int image_data_node_id() { return image_data_node_id_; }
+  void set_image_data_node_id(int id) { image_data_node_id_ = id; }
+
+  void set_max_image_data_size(const gfx::Size& size) {
+    max_image_data_size_ = size;
+  }
+
   // Set the id of the node with accessibility focus. The node with
   // accessibility focus will force loading inline text box children,
   // which aren't always loaded by default on all platforms.
@@ -100,10 +112,15 @@ class BlinkAXTreeSource
   blink::WebAXObject explicit_root_;
 
   // The id of the object with accessibility focus.
-  int accessibility_focus_id_;
+  int accessibility_focus_id_ = -1;
+
+  // The id of the object to fetch image data for.
+  int image_data_node_id_ = -1;
+
+  gfx::Size max_image_data_size_;
 
   // These are updated when calling |Freeze|.
-  bool frozen_;
+  bool frozen_ = false;
   blink::WebDocument document_;
   blink::WebAXObject root_;
   blink::WebAXObject focus_;