TaskScheduler: Minor clarifications to SchedulerLock code

This is a follow-up to https://chromium-review.googlesource.com/c/chromium/src/+/1320650

Bug: 889029
Change-Id: I4dd60a56fcab509578cdfe08c999c1e34fd72375
Reviewed-on: https://chromium-review.googlesource.com/c/1331219
Commit-Queue: Jesse McKenna <jessemckenna@google.com>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607257}

base/task/task_scheduler/scheduler_lock.h

@@ -25,13 +25,15 @@ namespace internal {
 //     Default constructor, no predecessor lock.
 //     DCHECKs
 //         On Acquisition if any scheduler lock is acquired on this thread.
+//             Okay if a universal predecessor is acquired.
 //
 // SchedulerLock(const SchedulerLock* predecessor)
 //     Constructor that specifies an allowed predecessor for that lock.
 //     DCHECKs
 //         On Construction if |predecessor| forms a predecessor lock cycle.
 //         On Acquisition if the previous lock acquired on the thread is not
-//             |predecessor|. Okay if there was no previous lock acquired.
+//             either |predecessor| or a universal predecessor. Okay if there
+//             was no previous lock acquired.
 //
 // SchedulerLock(UniversalPredecessor universal_predecessor)
 //     Constructor for a lock that will allow the acquisition of any lock after

base/task/task_scheduler/scheduler_lock_impl.cc

@@ -64,12 +64,12 @@ class SafeAcquisitionTracker {
       return;
 
     // A universal predecessor may not be acquired after any other lock.
-    DCHECK(!lock->universal_predecessor());
+    DCHECK(!lock->is_universal_predecessor());
 
     // Otherwise, make sure that the previous lock acquired is either an
     // allowed predecessor for this lock or a universal predecessor.
     const SchedulerLockImpl* previous_lock = acquired_locks->back();
-    if (previous_lock->universal_predecessor())
+    if (previous_lock->is_universal_predecessor())
       return;
 
     AutoLock auto_lock(allowed_predecessor_map_lock_);
@@ -132,12 +132,12 @@ LazyInstance<SafeAcquisitionTracker>::Leaky g_safe_acquisition_tracker =
 SchedulerLockImpl::SchedulerLockImpl() : SchedulerLockImpl(nullptr) {}
 
 SchedulerLockImpl::SchedulerLockImpl(const SchedulerLockImpl* predecessor)
-    : universal_predecessor_(false) {
+    : is_universal_predecessor_(false) {
   g_safe_acquisition_tracker.Get().RegisterLock(this, predecessor);
 }
 
 SchedulerLockImpl::SchedulerLockImpl(UniversalPredecessor)
-    : universal_predecessor_(true) {}
+    : is_universal_predecessor_(true) {}
 
 SchedulerLockImpl::~SchedulerLockImpl() {
   g_safe_acquisition_tracker.Get().UnregisterLock(this);

base/task/task_scheduler/scheduler_lock_impl.h

@@ -37,11 +37,11 @@ class BASE_EXPORT SchedulerLockImpl {
 
   std::unique_ptr<ConditionVariable> CreateConditionVariable();
 
-  bool universal_predecessor() const { return universal_predecessor_; }
+  bool is_universal_predecessor() const { return is_universal_predecessor_; }
 
  private:
   Lock lock_;
-  const bool universal_predecessor_;
+  const bool is_universal_predecessor_;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerLockImpl);
 };