Make the assumption on the minimum buffer size for GetLogLines explicit.

src/log-utils.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 178 matching lines @@
   ASSERT(from_pos >= 0);
   ASSERT(max_size >= 0);
   int actual_size = output_buffer_->Read(from_pos, dest_buf, max_size);
   ASSERT(actual_size <= max_size);
   if (actual_size == 0) return 0;
 
   // Find previous log line boundary.
   char* end_pos = dest_buf + actual_size - 1;
   while (end_pos >= dest_buf && *end_pos != '\n') --end_pos;
   actual_size = static_cast<int>(end_pos - dest_buf + 1);
+  // If the assertion below is hit, it means that there was no line end
+  // found --- something wrong has happened.
+  ASSERT(actual_size > 0);
   ASSERT(actual_size <= max_size);
   return actual_size;
 }
 
 
 LogMessageBuilder::WriteFailureHandler
     LogMessageBuilder::write_failure_handler = NULL;
 
 
 LogMessageBuilder::LogMessageBuilder(): sl(Log::mutex_), pos_(0) {
@@ skipping 276 matching lines @@
     PrintBackwardReference(backref, best.distance, best.copy_from_pos);
     ASSERT(strlen(backref.start()) - best.backref_size == 0);
     prev_record->Truncate(static_cast<int>(unchanged_len + best.backref_size));
   }
   return true;
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal