Split ProcessHandle and its related routines into base/process/process_handle.h.

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 849fbe023fa973a51891d838b6983cbdba5d6eac..21e5a5dcebecbfc8c2e0eba5b4707a08eecffd21 100644
--- a/base/process/process_metrics_linux.cc
+++ b/base/process/process_metrics_linux.cc
@@ -496,4 +496,11 @@ bool GetSystemMemoryInfo(SystemMemoryInfoKB* meminfo) {
   return true;
 }
 
+const char kProcSelfExe[] = "/proc/self/exe";
+
+int GetNumberOfThreads(ProcessHandle process) {
+  return internal::ReadProcStatsAndGetFieldAsInt(process,
+                                                 internal::VM_NUMTHREADS);
+}
+
 }  // namespace base