base/process: Use /proc/self/stat to read startup time.

base/process/internal_linux.cc

Index: base/process/internal_linux.cc
diff --git a/base/process/internal_linux.cc b/base/process/internal_linux.cc
index e9ed641dc02909c4b4edea18be5508c630c5527f..47d113ad77268addeb47c4f4e443dd5b7690bdd8 100644
--- a/base/process/internal_linux.cc
+++ b/base/process/internal_linux.cc
@@ -133,6 +133,18 @@ size_t GetProcStatsFieldAsSizeT(const std::vector<std::string>& proc_stats,
   return StringToSizeT(proc_stats[field_num], &value) ? value : 0;
 }
 
+int64_t ReadProcStatsAndGetFieldAsInt64(const std::string& pid,
+                                        ProcStatsFields field_num) {
+  std::string stats_data;
+  FilePath stat_file = FilePath(kProcDir).Append(pid).Append(kStatFile);
+  if (!ReadProcFile(stat_file, &stats_data))
+    return 0;
+  std::vector<std::string> proc_stats;

[jln (very slow on Chromium), 2017/02/22 22:37:15]

A little too much code duplication here. Perhaps refactor a tad if it's worth
it?  Up to you.

[Daniele Castagna, 2017/02/23 18:04:10]

Done.

+  if (!ParseProcStats(stats_data, &proc_stats))
+    return 0;
+  return GetProcStatsFieldAsInt64(proc_stats, field_num);
+}
+
 int64_t ReadProcStatsAndGetFieldAsInt64(pid_t pid, ProcStatsFields field_num) {
   std::string stats_data;
   if (!ReadProcStats(pid, &stats_data))