A video tag should play content src is set asynchronously with preload is disabled.

third_party/WebKit/Source/core/html/HTMLMediaElement.h

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights
  * reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 608 matching lines @@
   mutable double official_playback_position_;
   mutable bool official_playback_position_needs_update_;
 
   double fragment_end_time_;
 
   typedef unsigned PendingActionFlags;
   PendingActionFlags pending_action_flags_;
 
   // FIXME: HTMLMediaElement has way too many state bits.
   bool playing_ : 1;
+  bool pending_play_ : 1;
   bool should_delay_load_event_ : 1;
   bool have_fired_loaded_data_ : 1;
   bool can_autoplay_ : 1;
   bool muted_ : 1;
   bool paused_ : 1;
   bool seeking_ : 1;
 
   // data has not been loaded since sending a "stalled" event
   bool sent_stalled_event_ : 1;
 
@@ skipping 102 matching lines @@
 
 inline bool IsHTMLMediaElement(const HTMLElement& element) {
   return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 }  // namespace blink
 
 #endif  // HTMLMediaElement_h