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

chrome/common/extensions/api/automation.idl

 // Copyright 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.
 
 // The <code>chrome.automation</code> API allows developers to access the
 // automation (accessibility) tree for the browser. The tree resembles the DOM
 // tree, but only exposes the <em>semantic</em> structure of a page. It can be
 // used to programmatically interact with a page by examining names, roles, and
 // states, listening for events, and performing actions on nodes.
 [nocompile] namespace automation {
   // Keep the following enums in sync with 'ui/accessibility/ax_enums.idl'.
   // They are kept here purely for extension docs generation.
 
   // Possible events fired on an $(ref:automation.AutomationNode).
   enum EventType {
     activedescendantchanged,
     alert,
     ariaAttributeChanged,
     autocorrectionOccured,
     blur,
     checkedStateChanged,
     childrenChanged,
     clicked,
     documentSelectionChanged,
     expandedChanged,
     focus,
+    imageFrameUpdated,
     hide,
     hover,
     invalidStatusChanged,
     layoutComplete,
     liveRegionCreated,
     liveRegionChanged,
     loadComplete,
     locationChanged,
     menuEnd,
     menuListItemSelected,
@@ skipping 531 matching lines @@
 
     // Does the default action based on this node's role. This is generally
     // the same action that would result from clicking the node such as
     // expanding a treeitem, toggling a checkbox, selecting a radiobutton,
     // or activating a button.
     static void doDefault();
 
     // Places focus on this node.
     static void focus();
 
+    // Request a data url for the contents of an image, optionally
+    // resized.  Pass zero for maxWidth and/or maxHeight for the
+    // original size.
+    static void getImageData(long maxWidth, long maxHeight);
+
     // Scrolls this node to make it visible.
     static void makeVisible();
 
     // Sets selection within a text field.
     static void setSelection(long startIndex, long endIndex);
 
     // Clears focus and sets this node as the starting point for the next
     // time the user presses Tab or Shift+Tab.
     static void setSequentialFocusNavigationStartingPoint();
 
@@ skipping 71 matching lines @@
     // Everything in the tree between the two node/offset pairs gets included
     // in the selection. The anchor is where the user started the selection,
     // while the focus is the point at which the selection gets extended
     // e.g. when dragging with a mouse or using the keyboard. For nodes with
     // the role staticText, the offset gives the character offset within
     // the value where the selection starts or ends, respectively.
     [nocompile] static void setDocumentSelection(
         SetDocumentSelectionParams params);
   };
 };