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

chrome/renderer/resources/extensions/automation/automation_node.js

Index: chrome/renderer/resources/extensions/automation/automation_node.js
diff --git a/chrome/renderer/resources/extensions/automation/automation_node.js b/chrome/renderer/resources/extensions/automation/automation_node.js
index 2da36e205a7d8ea70ee413dc6167304c65836afb..8bcaf3b93950e93a6af993310b7d8896bac6fe81 100644
--- a/chrome/renderer/resources/extensions/automation/automation_node.js
+++ b/chrome/renderer/resources/extensions/automation/automation_node.js
@@ -367,6 +367,12 @@ AutomationNodeImpl.prototype = {
     this.performAction_('focus');
   },
 
+  getImageData: function(maxWidth, maxHeight) {
+    this.performAction_('getImageData',
+                        { maxWidth: maxWidth,
+                          maxHeight: maxHeight });
+  },
+
   makeVisible: function() {
     this.performAction_('makeVisible');
   },
@@ -657,6 +663,7 @@ var stringAttributes = [
     'dropeffect',
     'help',
     'htmlTag',
+    'imageDataUrl',
     'language',
     'liveRelevant',
     'liveStatus',
@@ -1061,6 +1068,7 @@ utils.expose(AutomationNode, AutomationNodeImpl, {
     'find',
     'findAll',
     'focus',
+    'getImageData',
     'makeVisible',
     'matches',
     'setSelection',