make debug mode ~20% faster on linux

base/threading/platform_thread_posix.cc

Index: base/threading/platform_thread_posix.cc
diff --git a/base/threading/platform_thread_posix.cc b/base/threading/platform_thread_posix.cc
index 5b609c1a9870ed4c397944a25bb08319711096b6..a33e6097176af1c8406a77949127e3545178a1c1 100644
--- a/base/threading/platform_thread_posix.cc
+++ b/base/threading/platform_thread_posix.cc
@@ -149,7 +149,7 @@ PlatformThreadId PlatformThread::CurrentId() {
 #if defined(OS_MACOSX)
   return pthread_mach_thread_np(pthread_self());
 #elif defined(OS_LINUX)
-  return syscall(__NR_gettid);
+  return pthread_self();

[piman, 2014/05/20 05:09:22]

On my system, PlatformThreadId (a pid_t currently) is an int, whereas pthread_t
is an unsigned long int.

Can we change the definition of PlatformThreadId into a pthread_t on OS_LINUX?

 #elif defined(OS_ANDROID)
   return gettid();
 #elif defined(OS_SOLARIS) || defined(OS_QNX)