Fix typo in memory_dump_manager.cc

base/trace_event/memory_dump_manager.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/memory_dump_manager.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/atomic_sequence_num.h"
@@ skipping 181 matching lines @@
     const MemoryDumpProvider::Options& options) {
   if (dumper_registrations_ignored_for_testing_)
     return;
 
   scoped_refptr<MemoryDumpProviderInfo> mdpinfo =
       new MemoryDumpProviderInfo(mdp, name, task_runner, options);
 
   {
     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;
   }
 
   if (heap_profiling_enabled_)
     mdp->OnHeapProfilingEnabled(true);
 }
 
 void MemoryDumpManager::RegisterDumpProvider(
@@ skipping 404 matching lines @@
   auto iter = process_dumps.find(pid);
   if (iter == process_dumps.end()) {
     scoped_ptr<ProcessMemoryDump> new_pmd(new ProcessMemoryDump(session_state));
     iter = process_dumps.insert(std::make_pair(pid, std::move(new_pmd))).first;
   }
   return iter->second.get();
 }
 
 }  // namespace trace_event
 }  // namespace base