Reland "[ Observatory ] Disable serving Observatory by default"

This reverts commit 5a8ddc0756.

Reason for reland: fix for failing Flutter test landed upstream
in https://github.com/flutter/flutter/pull/122419

TEST=pkg/dartdev/test/commands/run_test.dart

Change-Id: I1152296828428e118ccba11025f25f6b1dbbb0f3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/290921
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>

CHANGELOG.md

@@ -168,6 +168,11 @@
 
 ### Tools
 
+#### Observatory
+- Observatory is no longer served by default and users should instead use Dart
+  DevTools. Users requiring specific functionality in Observatory should set
+  the `--serve-observatory` flag.
+
 #### Web Dev Compiler (DDC)
 - Removed deprecated command line flags `-k`, `--kernel`, and `--dart-sdk`.
 

pkg/dartdev/test/commands/run_test.dart

@@ -641,7 +641,7 @@ void main(List<String> args) => print("$b $args");
             '--enable-vm-service=0',
             if (!withDds) '--no-dds',
             if (!enableAuthCodes) '--disable-service-auth-codes',
-            if (!serve) '--no-serve-observatory',
+            if (serve) '--serve-observatory',
             p.relativeFilePath,
           ]);
 

runtime/bin/main_impl.cc

@@ -558,7 +558,7 @@ static Dart_Isolate CreateAndSetupServiceIsolate(const char* script_uri,
           Options::vm_service_auth_disabled(),
           Options::vm_write_service_info_filename(), Options::trace_loading(),
           Options::deterministic(), Options::enable_service_port_fallback(),
-          wait_for_dds_to_advertise_service, !Options::disable_observatory())) {
+          wait_for_dds_to_advertise_service, Options::enable_observatory())) {
     *error = Utils::StrDup(VmService::GetErrorMessage());
     return NULL;
   }

runtime/bin/main_options.h

@@ -49,7 +49,8 @@ namespace bin {
   V(bypass_trusting_system_roots, bypass_trusting_system_roots)                \
   V(delayed_filewatch_callback, delayed_filewatch_callback)                    \
   V(mark_main_isolate_as_system_isolate, mark_main_isolate_as_system_isolate)  \
-  V(no_serve_observatory, disable_observatory)
+  V(no_serve_observatory, disable_observatory)                                 \
+  V(serve_observatory, enable_observatory)
 
 // Boolean flags that have a short form.
 #define SHORT_BOOL_OPTIONS_LIST(V)                                             \

sdk/lib/_internal/vm/bin/vmservice_io.dart

@@ -40,7 +40,7 @@ bool _enableServicePortFallback = false;
 @pragma("vm:entry-point")
 bool _waitForDdsToAdvertiseService = false;
 @pragma("vm:entry-point", !const bool.fromEnvironment('dart.vm.product'))
-bool _serveObservatory = true;
+bool _serveObservatory = false;
 
 // HTTP server.
 Server? server;