[tracing] Send smaps file desciptor to child process for tracing

base/trace_event/process_memory_maps_dump_provider.cc

Index: base/trace_event/process_memory_maps_dump_provider.cc
diff --git a/base/trace_event/process_memory_maps_dump_provider.cc b/base/trace_event/process_memory_maps_dump_provider.cc
index 19f8d891618c10be3ae1d7a65d088b7aecacfb42..929a5090bcc009691ea7138dafb2a713895a15c8 100644
--- a/base/trace_event/process_memory_maps_dump_provider.cc
+++ b/base/trace_event/process_memory_maps_dump_provider.cc
@@ -4,7 +4,6 @@
 
 #include "base/trace_event/process_memory_maps_dump_provider.h"
 
-#include "base/files/scoped_file.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/strings/string_util.h"
@@ -141,11 +140,9 @@ ProcessMemoryMapsDumpProvider* ProcessMemoryMapsDumpProvider::GetInstance() {
                    LeakySingletonTraits<ProcessMemoryMapsDumpProvider>>::get();
 }
 
-ProcessMemoryMapsDumpProvider::ProcessMemoryMapsDumpProvider() {
-}
+ProcessMemoryMapsDumpProvider::ProcessMemoryMapsDumpProvider() {}
 
-ProcessMemoryMapsDumpProvider::~ProcessMemoryMapsDumpProvider() {
-}
+ProcessMemoryMapsDumpProvider::~ProcessMemoryMapsDumpProvider() {}
 
 // Called at trace dump point time. Creates a snapshot of the memory maps for
 // the current process.
@@ -158,9 +155,11 @@ bool ProcessMemoryMapsDumpProvider::OnMemoryDump(const MemoryDumpArgs& args,
   uint32 res = 0;
   if (UNLIKELY(proc_smaps_for_testing)) {
     res = ReadLinuxProcSmapsFile(proc_smaps_for_testing, pmd->process_mmaps());
+  } else if (smaps_file_) {
+    res = ReadLinuxProcSmapsFile(smaps_file_.get(), pmd->process_mmaps());
   } else {
-    ScopedFILE smaps_file(fopen("/proc/self/smaps", "r"));
-    res = ReadLinuxProcSmapsFile(smaps_file.get(), pmd->process_mmaps());
+    ScopedFILE file(fopen("/proc/self/smaps", "r"));
+    res = ReadLinuxProcSmapsFile(file.get(), pmd->process_mmaps());
   }
 
   if (res > 0) {