Add event params to AXTreeUpdate::ToString

R=nektar@chromium.org

AX-Relnotes: n/a
Change-Id: I1d4d8e51f6998b76a8894991e05c5bfc05bb2b9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2211057Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771650}

ui/accessibility/ax_tree_update.h

@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "base/strings/string_number_conversions.h"
+#include "ui/accessibility/ax_enum_util.h"
 #include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/accessibility/ax_event_intent.h"
 #include "ui/accessibility/ax_node_data.h"
@@ -104,6 +105,16 @@ std::string AXTreeUpdateBase<AXNodeData, AXTreeData>::ToString() const {
     result += "AXTreeUpdate: root id " + base::NumberToString(root_id) + "\n";
   }
 
+  if (event_from != ax::mojom::EventFrom::kNone)
+    result += "event_from=" + std::string(ui::ToString(event_from)) + "\n";
+
+  if (!event_intents.empty()) {
+    result += "event_intents=[\n";
+    for (const auto& event_intent : event_intents)
+      result += "  " + event_intent.ToString() + "\n";
+    result += "]\n";
+  }
+
   // The challenge here is that we want to indent the nodes being updated
   // so that parent/child relationships are clear, but we don't have access
   // to the rest of the tree for context, so we have to try to show the