Added Tab.SnapshotContent and MapsGL example to telemetry

tools/telemetry/examples/mapsgl_single_run_basic_expectations.json

 [
   {
-    // green forest
+    "comment": "green forest",
     "location": [ 300, 300 ],
     "color": [ 201, 223, 175 ],
     "tolerance": 3
   },
   {
-    // blue lake
+    "comment": "blue lake",
     "location": [ 712, 489 ],
     "color": [ 165, 191, 221 ],
     "tolerance": 3
   },
   {
-    // dark background
+    "comment": "dark background",
     "location": [ 900, 400 ],
     "color": [ 240, 237, 229 ],
     "tolerance": 3
   },
   {
-    // light background
+    "comment": "light background",
     "location": [ 650, 300 ],
     "color": [ 244, 243, 240 ],
     "tolerance": 3
-  },
-]
+  }
+]