Report trace buffer usage as number of events, not only percentage

components/tracing/child_trace_message_filter.cc

Index: components/tracing/child_trace_message_filter.cc
diff --git a/components/tracing/child_trace_message_filter.cc b/components/tracing/child_trace_message_filter.cc
index fe13ff57dd08ca8d7038c7c38ad091bafa18e145..f051c0f8f688856e506d694448a28acc7c067dc6 100644
--- a/components/tracing/child_trace_message_filter.cc
+++ b/components/tracing/child_trace_message_filter.cc
@@ -36,8 +36,7 @@ bool ChildTraceMessageFilter::OnMessageReceived(const IPC::Message& message) {
     IPC_MESSAGE_HANDLER(TracingMsg_DisableMonitoring, OnDisableMonitoring)
     IPC_MESSAGE_HANDLER(TracingMsg_CaptureMonitoringSnapshot,
                         OnCaptureMonitoringSnapshot)
-    IPC_MESSAGE_HANDLER(TracingMsg_GetTraceBufferPercentFull,
-                        OnGetTraceBufferPercentFull)
+    IPC_MESSAGE_HANDLER(TracingMsg_GetTraceBufferUsage, OnGetTraceBufferUsage)
     IPC_MESSAGE_HANDLER(TracingMsg_SetWatchEvent, OnSetWatchEvent)
     IPC_MESSAGE_HANDLER(TracingMsg_CancelWatchEvent, OnCancelWatchEvent)
     IPC_MESSAGE_UNHANDLED(handled = false)
@@ -105,10 +104,14 @@ void ChildTraceMessageFilter::OnCaptureMonitoringSnapshot() {
                  this));
 }
 
-void ChildTraceMessageFilter::OnGetTraceBufferPercentFull() {
-  float bpf = TraceLog::GetInstance()->GetBufferPercentFull();
+void ChildTraceMessageFilter::OnGetTraceBufferUsage() {
+  float buffer_percent_full;
+  size_t approximate_event_count;
+  TraceLog::GetInstance()->GetBufferUsage(&buffer_percent_full,
+                                          &approximate_event_count);
 
-  sender_->Send(new TracingHostMsg_TraceBufferPercentFullReply(bpf));
+  sender_->Send(new TracingHostMsg_TraceBufferUsageReply(
+      buffer_percent_full, approximate_event_count));
 }
 
 void ChildTraceMessageFilter::OnSetWatchEvent(const std::string& category_name,