Use portable typedef for PIDs (process IDs).

base/process_util_posix.cc

Index: base/process_util_posix.cc
diff --git a/base/process_util_posix.cc b/base/process_util_posix.cc
index 37888d51dacf4eb89d464f63a50e0a0fd419327f..439b8060354e3a4f5ce4ac3fb1b232cf7ec38b6f 100644
--- a/base/process_util_posix.cc
+++ b/base/process_util_posix.cc
@@ -27,7 +27,7 @@ const int kMicrosecondsPerSecond = 1000000;
 
 namespace base {
 
-int GetCurrentProcId() {
+ProcessId GetCurrentProcId() {
   return getpid();
 }
 
@@ -35,7 +35,7 @@ ProcessHandle GetCurrentProcessHandle() {
   return GetCurrentProcId();
 }
 
-ProcessHandle OpenProcessHandle(int pid) {
+ProcessHandle OpenProcessHandle(ProcessId pid) {
   // On Posix platforms, process handles are the same as PIDs, so we
   // don't need to do anything.
   return pid;
@@ -46,7 +46,7 @@ void CloseProcessHandle(ProcessHandle process) {
   return;
 }
 
-int GetProcId(ProcessHandle process) {
+ProcessId GetProcId(ProcessHandle process) {
   return process;
 }