Use auto& instead of auto in the range loop

There are a couple reasons for this change:
1. Avoid copying a struct larger than a pointer.
2. If the pointer in the struct gets replaced by CheckedPtr with
   a non-trivial constructor, the compiler will complain.

See go/miracleptr for more details on the experimental CheckedPtr project.

Bug: 1080832
Change-Id: I5d0718a351af253bd3917bef87d417f9f0d71b17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435033
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811485}

content/browser/accessibility/browser_accessibility_manager.cc

@@ -1368,7 +1368,7 @@ void BrowserAccessibilityManager::OnAtomicUpdateFinished(
   }
 
   // Calls OnDataChanged on newly created, reparented or changed nodes.
-  for (const auto change : changes) {
+  for (const auto& change : changes) {
     ui::AXNode* node = change.node;
     BrowserAccessibility* wrapper = GetFromAXNode(node);
     if (wrapper) {