[fuchsia][a11y] Remove attempt to "clear" a11y bridge inspect node.

We try to ensure that the AXTree dump inspect node is only inflated when
semantics are enabled by resetting the node's value to inspect::LazyNode().
However, doing so doesn't actually dissociate the old callback from the
node, so the old callback will still run on subsequent queries. It's
unclear whether the issue affects prod, but it can cause crashes on dev
builds.

Instead of attempting to "clear" the LazyNode when semantic updates are
disabled, I think it's best to leave it intact. We still clear ax_trees_
when semantic updates are disabled, so the node will not produce any
output when semantic updates are disabled (which is the desired
outcome).

(cherry picked from commit 2f4262b)

Test: manually verified on device
Bug: fuchsia:91565
Change-Id: Ib82259ce033bd1b79ea8e6a7204613a804c7ac92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3389996
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#989614}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3575363
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Srinivas Sista <srinivassista@chromium.org>
Commit-Queue: Srinivas Sista <srinivassista@chromium.org>
Cr-Commit-Position: refs/branch-heads/4692@{#1550}
Cr-Branched-From: 038cd96-refs/heads/main@{#938553}

fuchsia/engine/browser/accessibility_bridge.cc

@@ -71,11 +71,14 @@ AccessibilityBridge::AccessibilityBridge(
     ZX_LOG(ERROR, status) << "SemanticTree disconnected";
     std::move(on_error_callback_).Run(ZX_ERR_INTERNAL);
   });
+
+  // Set up inspect node for semantic trees.
+  inspect_node_tree_dump_ = inspect_node_.CreateLazyNode(
+      kSemanticTreesInspectNodeName,
+      [this]() { return fit::make_ok_promise(FillInspectData()); });
 }
 
 inspect::Inspector AccessibilityBridge::FillInspectData() {
-  DCHECK(enable_semantic_updates_);
-
   inspect::Inspector inspector;
 
   // Add a node for each AXTree of which the accessibility bridge is aware.
@@ -310,10 +313,6 @@ void AccessibilityBridge::OnSemanticsModeChanged(
     // The first call to AccessibilityEventReceived after this call will be
     // the entire semantic tree.
     web_contents_->EnableWebContentsOnlyAccessibilityMode();
-    // Set up inspect node for semantic trees.
-    inspect_node_tree_dump_ = inspect_node_.CreateLazyNode(
-        kSemanticTreesInspectNodeName,
-        [this]() { return fit::make_ok_promise(FillInspectData()); });
   } else {
     // The SemanticsManager will clear all state in this case, which is
     // mirrored here.
@@ -327,7 +326,6 @@ void AccessibilityBridge::OnSemanticsModeChanged(
     tree_connections_.clear();
     frame_id_to_tree_id_.clear();
     InterruptPendingActions();
-    inspect_node_tree_dump_ = inspect::LazyNode();
   }
 
   // Notify the SemanticsManager that this request was handled.