Update from https://crrev.com/333737

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 d8f06e5884d559682660f8aedf73938473886c59..3468f45f91efd4929ea838f91559251a2d75a4ef 100644
--- a/base/threading/platform_thread.h
+++ b/base/threading/platform_thread.h
@@ -89,6 +89,10 @@ class PlatformThreadHandle {
         id_(id) {
   }
 
+  PlatformThreadId id() const {
+    return id_;
+  }
+
   bool is_equal(const PlatformThreadHandle& other) const {
     return handle_ == other.handle_;
   }
@@ -102,8 +106,6 @@ class PlatformThreadHandle {
   }
 
  private:
-  friend class PlatformThread;
-
   Handle handle_;
   PlatformThreadId id_;
 };
@@ -190,6 +192,11 @@ class BASE_EXPORT PlatformThread {
   // |thread_handle|.
   static void Join(PlatformThreadHandle thread_handle);
 
+  // Toggles the target thread's priority at runtime.  Prefer
+  // CreateWithPriority() to set the thread's initial priority.
+  // NOTE: The call may fail if the caller thread is not the same as the
+  // target thread on POSIX.  For example, seccomp-bpf blocks it by default
+  // in the sandbox.
   static void SetThreadPriority(PlatformThreadHandle handle,
                                 ThreadPriority priority);