Bulk Reports: Fix an infinite loop in ChildTraceMessageFilter::OnSetUMACallback.

components/tracing/child_trace_message_filter.h

Index: components/tracing/child_trace_message_filter.h
diff --git a/components/tracing/child_trace_message_filter.h b/components/tracing/child_trace_message_filter.h
index 9f7755ca70d2638a009fb72d4526f244af67dd92..47999762f944bda0b6d486442450ef3da51f8515 100644
--- a/components/tracing/child_trace_message_filter.h
+++ b/components/tracing/child_trace_message_filter.h
@@ -42,6 +42,8 @@ class TRACING_EXPORT ChildTraceMessageFilter : public IPC::MessageFilter {
   ~ChildTraceMessageFilter() override;
 
  private:
+  friend class ChildTraceMessageFilterTest;
+
   // Message handlers.
   void OnBeginTracing(const std::string& trace_config_str,
                       base::TimeTicks browser_time,
@@ -84,6 +86,8 @@ class TRACING_EXPORT ChildTraceMessageFilter : public IPC::MessageFilter {
 
   void OnProcessMemoryDumpDone(uint64 dump_guid, bool success);
 
+  void SetSenderForTesting(IPC::Sender* sender);
+
   IPC::Sender* sender_;
   base::SingleThreadTaskRunner* ipc_task_runner_;