[tracing] Dump child processes' memory metrics in browser

content/browser/tracing/trace_message_filter.cc

Index: content/browser/tracing/trace_message_filter.cc
diff --git a/content/browser/tracing/trace_message_filter.cc b/content/browser/tracing/trace_message_filter.cc
index a8a3caf3badee2825b7b80c3afd11306621e88e6..3bc6db19e3526bca565918de7f2114490228763c 100644
--- a/content/browser/tracing/trace_message_filter.cc
+++ b/content/browser/tracing/trace_message_filter.cc
@@ -36,6 +36,8 @@ void TraceMessageFilter::OnChannelClosing() {
       OnTraceLogStatusReply(base::trace_event::TraceLogStatus());
 
     TracingControllerImpl::GetInstance()->RemoveTraceMessageFilter(this);
+    base::trace_event::MemoryDumpManager::GetInstance()
+        ->UnregisterProcessMetricsProvidersFor(peer_pid());
   }
 }
 
@@ -140,6 +142,8 @@ void TraceMessageFilter::SendGlobalMemoryDumpResponse(uint64 dump_guid,
 void TraceMessageFilter::OnChildSupportsTracing() {
   has_child_ = true;
   TracingControllerImpl::GetInstance()->AddTraceMessageFilter(this);
+  base::trace_event::MemoryDumpManager::GetInstance()
+      ->RegisterProcessMetricsProvidersFor(peer_pid());
 }
 
 void TraceMessageFilter::OnEndTracingAck(