[tracing] Dump child processes' memory metrics in browser

base/process/process_metrics_linux.cc

 // Copyright (c) 2013 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.
 
 #include "base/process/process_metrics.h"
 
 #include <dirent.h>
 #include <fcntl.h>
 #include <stddef.h>
 #include <stdint.h>
@@ skipping 68 matching lines @@
         return 0;
       }
       size_t value;
       if (!StringToSizeT(split_value_str[0], &value)) {
         NOTREACHED();
         return 0;
       }
       return value;
     }
   }
-  NOTREACHED();

[Primiano Tucci (use gerrit), 2016/01/05 11:55:17]

hmm if you do this I think you need to turn this into a function that returns a
bool and puts the value into a out ptr.
I mean:

bool  ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field,
size_t* value)

There are only two places that use ReadProcStatus...., you can move the DCHECK
to those places

[ssid, 2016/01/06 20:26:33]

I think this dcheck should not exist since it is okay to fail here. Sometimes
status does not give the values needed. And the only place which uses this
method is our code in dump provider. Now I made it bool and to fail in
GetPeakPageFileUsage and not fail in GetPeakWorkingSetSize

   return 0;
 }
 
 #if defined(OS_LINUX)
 // Read /proc/<pid>/sched and look for |field|. On succes, return true and
 // write the value for |field| into |result|.
 // Only works for fields in the form of "field    :     uint_value"
 bool ReadProcSchedAndGetFieldAsUint64(pid_t pid,
                                       const std::string& field,
                                       uint64_t* result) {
@@ skipping 841 matching lines @@
 #if defined(OS_LINUX)
 int ProcessMetrics::GetIdleWakeupsPerSecond() {
   uint64_t wake_ups;
   const char kWakeupStat[] = "se.statistics.nr_wakeups";
   return ReadProcSchedAndGetFieldAsUint64(process_, kWakeupStat, &wake_ups) ?
       CalculateIdleWakeupsPerSecond(wake_ups) : 0;
 }
 #endif  // defined(OS_LINUX)
 
 }  // namespace base