Un-ignore UnretainedWrapper::ptr_

We want to protect it. It doesn't seem to cause crashes that
we've seen in the past and perfornce doesn't regress with BRP.

Bug: 1141567, 1069567
Change-Id: I29b05dfe188961c26287138009e1fdf70f871d92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2509870Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822880}

tools/clang/rewrite_raw_ptr_fields/manual-fields-to-ignore.txt

@@ -143,7 +143,6 @@ performance_manager::frame_priority::BoostingVoteAggregator::Edge::dst_
 
 # Populated manually - these pointers crash due to a mismatching tag.
 # Under investigation.
-base::internal::UnretainedWrapper::ptr_
 blink::NGPhysicalContainerFragment::buffer_
 blink::DisplayItem::client_
 cc::FrameSequenceMetrics::throughput_ukm_reporter_