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

components/tracing/tracing_messages.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Multiply-included message header, no traditional include guard.
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/sync_socket.h"
@@ skipping 19 matching lines @@
                      base::TimeTicks /* browser_time */,
                      std::string /* base::debug::TraceOptions */)
 
 // Sent to all child processes to stop monitoring.
 IPC_MESSAGE_CONTROL0(TracingMsg_DisableMonitoring)
 
 // Sent to all child processes to capture the current monitorint snapshot.
 IPC_MESSAGE_CONTROL0(TracingMsg_CaptureMonitoringSnapshot)
 
 // Sent to all child processes to get trace buffer fullness.
-IPC_MESSAGE_CONTROL0(TracingMsg_GetTraceBufferPercentFull)
+IPC_MESSAGE_CONTROL0(TracingMsg_GetTraceBufferUsage)
 
 // Sent to all child processes to set watch event.
 IPC_MESSAGE_CONTROL2(TracingMsg_SetWatchEvent,
                      std::string /* category_name */,
                      std::string /* event_name */)
 
 // Sent to all child processes to clear watch event.
 IPC_MESSAGE_CONTROL0(TracingMsg_CancelWatchEvent)
 
 // Sent everytime when a watch event is matched.
@@ skipping 11 matching lines @@
 
 // Child processes send back trace data in JSON chunks.
 IPC_MESSAGE_CONTROL1(TracingHostMsg_TraceDataCollected,
                      std::string /*json trace data*/)
 
 // Child processes send back trace data of the current monitoring
 // in JSON chunks.
 IPC_MESSAGE_CONTROL1(TracingHostMsg_MonitoringTraceDataCollected,
                      std::string /*json trace data*/)
 
-// Reply to TracingMsg_GetTraceBufferPercentFull.
-IPC_MESSAGE_CONTROL1(TracingHostMsg_TraceBufferPercentFullReply,
-                     float /*trace buffer percent full*/)
-
+// Reply to TracingMsg_GetTraceBufferUsage.
+IPC_MESSAGE_CONTROL2(TracingHostMsg_TraceBufferUsageReply,
+                     float /*trace buffer percent full*/,
+                     size_t /*trace buffer usage in number of events*/)