Revert of Remove DCHECK_IMPLIES/CHECK_IMPLIES.

base/trace_event/trace_log.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/trace_log.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/base_switches.h"
@@ skipping 861 matching lines @@
   int generation = this->generation();
   // Copy of thread_message_loops_ to be used without locking.
   std::vector<scoped_refptr<SingleThreadTaskRunner>>
       thread_message_loop_task_runners;
   {
     AutoLock lock(lock_);
     DCHECK(!flush_task_runner_);
     flush_task_runner_ = ThreadTaskRunnerHandle::IsSet()
                              ? ThreadTaskRunnerHandle::Get()
                              : nullptr;
-    DCHECK(!thread_message_loops_.size() || flush_task_runner_);
+    DCHECK_IMPLIES(thread_message_loops_.size(), flush_task_runner_);
     flush_output_callback_ = cb;
 
     if (thread_shared_chunk_) {
       logged_events_->ReturnChunk(thread_shared_chunk_index_,
                                   thread_shared_chunk_.Pass());
     }
 
     if (thread_message_loops_.size()) {
       for (hash_set<MessageLoop*>::const_iterator it =
                thread_message_loops_.begin();
@@ skipping 803 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_, name_,
                                                 event_handle_);
   }
 }
 
 }  // namespace trace_event_internal