[heap] Add a comment to persistent-handles.h

R=dinfuehr@chromium.org

Bug: v8:10315
Change-Id: I595bc76907c9f0f437d460916aec804b55895376
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2195822Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Auto-Submit: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67731}

src/handles/persistent-handles.h

@@ -17,6 +17,9 @@ namespace internal {
 
 class Heap;
 
+// PersistentHandles serves as a container for handles that can be passed back
+// and forth between threads. Allocation and deallocation of this class is
+// thread-safe and the isolate tracks all PersistentHandles containers.
 class PersistentHandles {
  public:
   V8_EXPORT_PRIVATE explicit PersistentHandles(

src/heap/safepoint.h

@@ -19,7 +19,7 @@ class LocalHeap;
 class RootVisitor;
 
 // Used to bring all background threads with heap access to a safepoint such
-// that e.g. a garabge collection can be performed.
+// that e.g. a garbage collection can be performed.
 class GlobalSafepoint {
  public:
   explicit GlobalSafepoint(Heap* heap);