Add a WebContentsImpl API to snapshot the accessibility tree.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 80bb605d5ae6ba2c40f13c9a46020f95f856ed1b..884a302506fda493e26710eb6804b31d6f5d72af 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -64,6 +64,7 @@
 #include "content/public/common/url_constants.h"
 #include "content/public/common/url_utils.h"
 #include "ui/accessibility/ax_tree.h"
+#include "ui/accessibility/ax_tree_update.h"
 #include "url/gurl.h"
 
 #if defined(OS_MACOSX)
@@ -381,6 +382,8 @@ bool RenderFrameHostImpl::OnMessageReceived(const IPC::Message &msg) {
                         OnAccessibilityLocationChanges)
     IPC_MESSAGE_HANDLER(AccessibilityHostMsg_FindInPageResult,
                         OnAccessibilityFindInPageResult)
+    IPC_MESSAGE_HANDLER(AccessibilityHostMsg_SnapshotResponse,
+                        OnAccessibilitySnapshotResponse)
     IPC_MESSAGE_HANDLER(FrameHostMsg_ToggleFullscreen, OnToggleFullscreen)
     // The following message is synthetic and doesn't come from RenderFrame, but
     // from RenderProcessHost.
@@ -1392,6 +1395,19 @@ void RenderFrameHostImpl::OnAccessibilityFindInPageResult(
   }
 }
 
+void RenderFrameHostImpl::OnAccessibilitySnapshotResponse(
+    int token,
+    const ui::AXTreeUpdate& snapshot) {
+  std::map<int, AXTreeSnapshotCallback>::iterator it =
+      ax_tree_snapshot_callbacks_.find(token);
+  if (it != ax_tree_snapshot_callbacks_.end()) {
+    it->second.Run(snapshot);
+    ax_tree_snapshot_callbacks_.erase(it);
+  } else {
+    NOTREACHED() << "Received AX tree snapshot response for unknown request";
+  }
+}
+
 void RenderFrameHostImpl::OnToggleFullscreen(bool enter_fullscreen) {
   if (enter_fullscreen)
     delegate_->EnterFullscreenMode(GetLastCommittedURL().GetOrigin());
@@ -1805,6 +1821,14 @@ void RenderFrameHostImpl::SetAccessibilityMode(AccessibilityMode mode) {
   Send(new FrameMsg_SetAccessibilityMode(routing_id_, mode));
 }
 
+void RenderFrameHostImpl::RequestAXTreeSnapshot(
+    AXTreeSnapshotCallback callback) {
+  static int next_token = 1;
+  int token = next_token++;
+  Send(new AccessibilityMsg_SnapshotTree(routing_id_, token));
+  ax_tree_snapshot_callbacks_.insert(std::make_pair(token, callback));
+}
+
 void RenderFrameHostImpl::SetAccessibilityCallbackForTesting(
     const base::Callback<void(ui::AXEvent, int)>& callback) {
   accessibility_testing_callback_ = callback;