Fix typo in memory_dump_manager.cc

base/trace_event/memory_dump_manager.cc

Index: base/trace_event/memory_dump_manager.cc
diff --git a/base/trace_event/memory_dump_manager.cc b/base/trace_event/memory_dump_manager.cc
index f5c3c4feb4b91c8e6835a154239cc55979e476ef..35de5ef3dad0d58f62dffa4ac972ee1678fe1456 100644
--- a/base/trace_event/memory_dump_manager.cc
+++ b/base/trace_event/memory_dump_manager.cc
@@ -199,7 +199,7 @@ void MemoryDumpManager::RegisterDumpProvider(
   {
     AutoLock lock(lock_);
     bool already_registered = !dump_providers_.insert(mdpinfo).second;
-    // This actually happen in some tests which don't have a clean tear-down
+    // This actually happens in some tests which don't have a clean tear-down
     // path for RenderThreadImpl::Init().
     if (already_registered)
       return;