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

content/renderer/accessibility/render_accessibility_impl.cc

Index: content/renderer/accessibility/render_accessibility_impl.cc
diff --git a/content/renderer/accessibility/render_accessibility_impl.cc b/content/renderer/accessibility/render_accessibility_impl.cc
index f6a4b851e1035e690534a4247c96f65455689f37..f6e7b482423b3040f45985c9060ca4c3f8b802d1 100644
--- a/content/renderer/accessibility/render_accessibility_impl.cc
+++ b/content/renderer/accessibility/render_accessibility_impl.cc
@@ -459,6 +459,9 @@ void RenderAccessibilityImpl::OnPerformAction(
     case ui::AX_ACTION_DO_DEFAULT:
       target.performDefaultAction();
       break;
+    case ui::AX_ACTION_GET_IMAGE_DATA:
+      OnGetImageData(target, data.target_rect.size());
+      break;
     case ui::AX_ACTION_HIT_TEST:
       OnHitTest(data.target_point);
       break;
@@ -574,6 +577,23 @@ void RenderAccessibilityImpl::OnSetAccessibilityFocus(
   HandleAXEvent(obj, ui::AX_EVENT_TREE_CHANGED);
 }
 
+void RenderAccessibilityImpl::OnGetImageData(
+    const blink::WebAXObject& obj, const gfx::Size& max_size) {
+  ScopedFreezeBlinkAXTreeSource freeze(&tree_source_);
+  if (tree_source_.image_data_node_id() == obj.axID())
+    return;
+
+  tree_source_.set_image_data_node_id(obj.axID());

[aboxhall, 2016/11/22 19:06:31]

Does this get reset to -1 at some point? Or will we continue to send down image
data for this node until we request image data for another one? Or does the tree
source fall out of scope at some point?

[dmazzoni, 2016/11/22 22:00:13]

It doesn't get reset currently, but the client could just call
it again with another node. If it's anything other than an image
it will have no effect, so you could just reset it to the root.

+  tree_source_.set_max_image_data_size(max_size);
+
+  const WebDocument& document = GetMainDocument();
+  if (document.isNull())
+    return;
+
+  serializer_.DeleteClientSubtree(obj);
+  HandleAXEvent(obj, ui::AX_EVENT_IMAGE_FRAME_UPDATED);
+}
+
 void RenderAccessibilityImpl::OnReset(int reset_token) {
   reset_token_ = reset_token;
   serializer_.Reset();