[tracing] Dump child processes' memory metrics in browser

base/process/process_metrics_linux.cc

Index: base/process/process_metrics_linux.cc
diff --git a/base/process/process_metrics_linux.cc b/base/process/process_metrics_linux.cc
index bcebcf5729fda730528c49119c3c58c19e0ac6dc..c556b4f7c1378ff9df223c4189656e8c40f0d5c5 100644
--- a/base/process/process_metrics_linux.cc
+++ b/base/process/process_metrics_linux.cc
@@ -53,16 +53,20 @@ static uint64_t ReadFileToUint64(const FilePath file) {
 }
 #endif
 
-// Read /proc/<pid>/status and return the value for |field|, or 0 on failure.
-// Only works for fields in the form of "Field: value kB".
-size_t ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field) {
+// Read /proc/<pid>/status and writes the value for |field| into |result|.
+// Returns true on success. Only works for fields in the form of
+// "Field: value kB".
+bool ReadProcStatusAndGetFieldAsSizeT(pid_t pid,
+                                      const std::string& field,
+                                      size_t* result) {
+  *result = 0;
   std::string status;
   {
     // Synchronously reading files in /proc does not hit the disk.
     ThreadRestrictions::ScopedAllowIO allow_io;
     FilePath stat_file = internal::GetProcPidDir(pid).Append("status");
     if (!ReadFileToString(stat_file, &status))
-      return 0;
+      return false;
   }
 
   StringPairs pairs;
@@ -76,18 +80,16 @@ size_t ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field) {
           value_str, " ", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
       if (split_value_str.size() != 2 || split_value_str[1] != "kB") {
         NOTREACHED();
-        return 0;
+        return false;
       }
-      size_t value;
-      if (!StringToSizeT(split_value_str[0], &value)) {
+      if (!StringToSizeT(split_value_str[0], result)) {
         NOTREACHED();
-        return 0;
+        return false;
       }
-      return value;
+      return true;
     }
   }
-  NOTREACHED();
-  return 0;
+  return false;
 }
 
 #if defined(OS_LINUX)
@@ -174,7 +176,10 @@ size_t ProcessMetrics::GetPagefileUsage() const {
 
 // On linux, we return the high water mark of vsize.
 size_t ProcessMetrics::GetPeakPagefileUsage() const {
-  return ReadProcStatusAndGetFieldAsSizeT(process_, "VmPeak") * 1024;
+  size_t value = 0;
+  bool res = ReadProcStatusAndGetFieldAsSizeT(process_, "VmPeak", &value);
+  DCHECK(res);
+  return value * 1024;
 }
 
 // On linux, we return RSS.
@@ -185,7 +190,9 @@ size_t ProcessMetrics::GetWorkingSetSize() const {
 
 // On linux, we return the high water mark of RSS.
 size_t ProcessMetrics::GetPeakWorkingSetSize() const {
-  return ReadProcStatusAndGetFieldAsSizeT(process_, "VmHWM") * 1024;
+  size_t value = 0;

[Primiano Tucci (use gerrit), 2016/01/07 11:34:35]

Oooh I see, you still cannot have the DCHECK here.
Super apologies, didn't get this.
At this point I think your previous proposal (just remove the dcheck) was better
and more consistent. 
Sorry for having you go back and forth here.

[ssid, 2016/01/07 13:03:09]

Done.

+  ReadProcStatusAndGetFieldAsSizeT(process_, "VmHWM", &value);
+  return value * 1024;
 }
 
 bool ProcessMetrics::GetMemoryBytes(size_t* private_bytes,