Add media perf benchamrk under network simulations.

tools/perf/page_sets/tough_video_cases.json

 {
   "description": "Video Stack Perf benchmark",
   "play-action": [
     { "action": "play",
       "wait_for_playing": true,
       "wait_for_ended": true
     }
   ],
   "seek_before_and_after_playhead": [
     { "action": "play",
@@ skipping 38 matching lines @@
       "url": "file://tough_video_cases/video.html?src=crowd.wav&type=audio",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
       "url": "file://tough_video_cases/video.html?src=crowd.ogg&type=audio",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=crowd1080.ogv&type=video",
+      "url": "file://tough_video_cases/video.html?src=crowd1080.ogv",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=crowd1080.webm&type=video",
+      "url": "file://tough_video_cases/video.html?src=crowd1080.webm",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=crowd2160.ogv&type=video",
+      "url": "file://tough_video_cases/video.html?src=crowd2160.ogv",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=crowd2160.webm&type=video",
+      "url": "file://tough_video_cases/video.html?src=crowd2160.webm",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
       "url": "file://tough_video_cases/video.html?src=tulip2.ogg&type=audio",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
       "url": "file://tough_video_cases/video.html?src=tulip2.wav&type=audio",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=tulip2.ogv&type=video",
+      "url": "file://tough_video_cases/video.html?src=tulip2.ogv",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=tulip2.webm&type=video",
+      "url": "file://tough_video_cases/video.html?src=tulip2.webm",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=crowd1080.mp4&type=video",
+      "url": "file://tough_video_cases/video.html?src=crowd1080.mp4",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=crowd2160.mp4&type=video",
+      "url": "file://tough_video_cases/video.html?src=crowd2160.mp4",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
       "url": "file://tough_video_cases/video.html?src=tulip2.mp3&type=audio",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
     {
-      "url": "file://tough_video_cases/video.html?src=tulip2.mp4&type=video",
+      "url": "file://tough_video_cases/video.html?src=tulip2.mp4",
       "media_metrics": {"action": "play-action"},
       "add_browser_metrics": true
     },
+    {
+      "url": "file://tough_video_cases/video.html?src=tulip2.m4a&type=audio",
+      "media_metrics": {"action": "play-action"},
+      "add_browser_metrics": true
+    },
     {
       "url": "file://tough_video_cases/video.html?src=tulip2.ogg&type=audio",
       "skip_basic_metrics": true,
       "media_metrics": {"action": "seek_before_and_after_playhead"}
     },
     {
       "url": "file://tough_video_cases/video.html?src=tulip2.wav&type=audio",
       "skip_basic_metrics": true,
       "media_metrics": {"action": "seek_before_and_after_playhead"}
     },
@@ skipping 22 matching lines @@
       "url": "file://tough_video_cases/audio_playback.html?id=single_audio",
       "media_metrics": {"action": "loop_single_audio"}
     },
     {
       "skip_basic_metrics": true,
       "url": "file://tough_video_cases/audio_playback.html?id=mixed_audio",
       "media_metrics": {"action": "loop_mixed_audio"}
     }
   ]
 }