Dart: Lazy observatory asset loading. Option to disable the observatory.

mojo/tools/data/benchmarks

 # This file contains a list of Mojo benchmarks. For description of the file
 # format, see `mojo_benchmark --help`.
 
 benchmarks = [
   {
     'name': 'dart init',
     'app': 'https://core.mojoapps.io/dart_startup.mojo',
     'duration': 10,
     'measurements': [
       {
@@ skipping 11 matching lines @@
     'app': 'https://core.mojoapps.io/dart_handler_running.mojo',
     'duration': 10,
     'measurements': [
       {
         'name': 'initialize',
         'spec': 'time_between/Dart/connecting/Dart/initialized',
       }
     ]
   },
   {
+    'name': 'dart init no observatory',
+    'app': 'https://core.mojoapps.io/dart_startup.mojo',
+    'duration': 10,
+    'measurements': [
+      {
+        'name': 'initialize',
+        'spec': 'time_until/Dart/initialized'
+      },
+      {
+        'name': 'accept connection',
+        'spec': 'time_between/Dart/initialized/Dart/connected',
+      }
+    ],
+    'shell-args': [
+      '--args-for=mojo:dart_content_handler --disable-observatory',
+    ]
+  },
+  {
     'name': 'cpp init',
     'app': 'https://core.mojoapps.io/trace_me.mojo',
     'duration': 10,
     'measurements': [
       {
         'name': 'initialize',
         'spec': 'time_until/trace_me/initialized',
       },
       {
         'name': 'accept connection',
         'spec': 'time_between/trace_me/initialized/trace_me/connected',
       }
     ],
     'shell-args': [
       '--args-for=https://core.mojoapps.io/trace_me.mojo --early-tracing',
     ]
   },
 ]