Make metrics state machine more lenient about OLD vs. CURRENT

chrome/common/metrics/metrics_log_manager.cc

 // Copyright (c) 2012 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 "chrome/common/metrics/metrics_log_manager.h"
 
 #if defined(USE_SYSTEM_LIBBZ2)
 #include <bzlib.h>
 #else
 #include "third_party/bzip2/bzlib.h"
@@ skipping 57 matching lines @@
   current_log_type_ = NO_LOG;
 }
 
 void MetricsLogManager::StageNextLogForUpload() {
   // Prioritize initial logs for uploading.
   std::vector<SerializedLog>* source_list =
       unsent_initial_logs_.empty() ? &unsent_ongoing_logs_
                                    : &unsent_initial_logs_;
   LogType source_type = (source_list == &unsent_ongoing_logs_) ? ONGOING_LOG
                                                                : INITIAL_LOG;
-  DCHECK(!source_list->empty());
+  // CHECK, rather than DCHECK, because swap()ing with an empty list causes
+  // hard-to-identify crashes much later.
+  CHECK(!source_list->empty());
   DCHECK(staged_log_text_.empty());
   DCHECK(staged_log_type_ == NO_LOG);
   staged_log_text_.swap(source_list->back());
   staged_log_type_ = source_type;
   source_list->pop_back();
 
   // If the staged log was the last provisional store, clear that.
   if (last_provisional_store_index_ != -1) {
     if (source_type == last_provisional_store_type_ &&
         static_cast<unsigned int>(last_provisional_store_index_) ==
@@ skipping 190 matching lines @@
     // TODO(jar): See if it would be better to do a CHECK() here.
     return false;
   }
   result = BZ2_bzCompressEnd(&stream);
   DCHECK(result == BZ_OK);
 
   output->resize(stream.total_out_lo32);
 
   return true;
 }