Make MediaSession per frame as an attribute of Navigator

third_party/WebKit/LayoutTests/VirtualTestSuites

 [
   {
     "prefix": "gpu",
     "base": "fast/canvas",
     "args": ["--enable-accelerated-2d-canvas",
              "--disable-display-list-2d-canvas"]
   },
   {
     "prefix": "display_list_2d_canvas",
     "base": "fast/canvas",
@@ skipping 155 matching lines @@
     "prefix": "scroll_customization",
     "base": "fast/events/touch",
     "args": ["--enable-blink-features=ScrollCustomization"]
   },
   {
     "prefix": "smoothscrolling",
     "base": "fast/events/touch/gesture",
     "args": ["--enable-smooth-scrolling"]
   },
   {
-    "prefix": "mediasession",
-    "base": "media/mediasession",
-    "args": ["--enable-blink-features=MediaSession"]
-  },
-  {
     "prefix": "mse-1mb-buffers",
     "base": "http/tests/media/media-source/stream_memory_tests",
     "args": ["--mse-audio-buffer-size-limit=1048576",
              "--mse-video-buffer-size-limit=1048576"]
   },
   {
     "prefix": "sharedarraybuffer",
     "base": "fast/workers",
     "args": ["--js-flags=--harmony-sharedarraybuffer",
              "--enable-blink-features=SharedArrayBuffer"]
@@ skipping 112 matching lines @@
     "prefix": "layout_ng",
     "base": "fast/block/basic",
     "args": ["--enable-blink-features=LayoutNG"]
   },
   {
     "prefix": "layout_ng",
     "base": "fast/block/margin-collapse",
     "args": ["--enable-blink-features=LayoutNG"]
   }
 ]