make debug mode ~20% faster on linux

base/threading/platform_thread.h

Index: base/threading/platform_thread.h
diff --git a/base/threading/platform_thread.h b/base/threading/platform_thread.h
index f2f3b260586cdcf67a75fae4b0a3e0119ece61f6..28743145610c70fe14f8c8fdd1e377a9aa861528 100644
--- a/base/threading/platform_thread.h
+++ b/base/threading/platform_thread.h
@@ -23,12 +23,48 @@
 
 namespace base {
 
+// Used for logging. Always an integer value.
 #if defined(OS_WIN)
 typedef DWORD PlatformThreadId;
 #elif defined(OS_POSIX)
 typedef pid_t PlatformThreadId;
 #endif
 
+// Used for thread checking and debugging.
+// Meant to be as fast as possible.
+// These are produced by PlatformThread::CurrentRef(), and used to later
+// check if we are on the same thread or not by using ==. These are safe
+// to copy between threads, but can't be copied to another process as they
+// have no meaning there. Also, the internal identifier can be re-used
+// after a thread dies, so a PlatformThreadRef cannot be reliably used
+// to distinguish a new thread from an old, dead thread.
+class PlatformThreadRef {
+ public:
+#if defined(OS_WIN)
+  typedef DWORD RefType;
+#elif defined(OS_POSIX)
+  typedef pthread_t RefType;
+#endif
+  PlatformThreadRef()
+      : id_(0) {
+  }
+
+  explicit PlatformThreadRef(RefType id)
+      : id_(id) {
+  }
+
+  bool operator==(PlatformThreadRef other) const {
+    return id_ == other.id_;
+  }
+
+  bool is_null() const {
+    return id_ == 0;
+  }
+ private:
+  RefType id_;
+};
+
+// Used to operate on threads.
 class PlatformThreadHandle {
  public:
 #if defined(OS_WIN)
@@ -101,6 +137,10 @@ class BASE_EXPORT PlatformThread {
   // Gets the current thread id, which may be useful for logging purposes.
   static PlatformThreadId CurrentId();
 
+  // Gets the current thread reference, which can be used to check if
+  // we're on the right thread quickly.
+  static PlatformThreadRef CurrentRef();
+
   // Get the current handle.
   static PlatformThreadHandle CurrentHandle();