add observatoryUrl property to FlutterEngine

shell/platform/darwin/ios/framework/Headers/FlutterEngine.h

@@ -228,6 +228,15 @@ FLUTTER_EXPORT
  */
 @property(nonatomic, readonly) FlutterBasicMessageChannel* settingsChannel;
 
+/**
+ * The `NSURL` of the observatory for the service isolate.
+ *
+ * This is only set in debug and profile runtime modes, and only after the
+ * observatory service is ready. In release mode or before the observatory has
+ * started, it returns `nil`.
+ */
+@property(nonatomic, readonly) NSURL* observatoryUrl;
+
 @end
 
 #endif  // FLUTTER_FLUTTERENGINE_H_

shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -207,6 +207,10 @@ - (FlutterBasicMessageChannel*)settingsChannel {
   return _settingsChannel.get();
 }
 
+- (NSURL*)observatoryUrl {
+  return [_publisher.get() url];
+}
+
 - (void)resetChannels {
   _localizationChannel.reset();
   _navigationChannel.reset();

shell/platform/darwin/ios/framework/Source/FlutterObservatoryPublisher.h

@@ -9,6 +9,8 @@
 
 @interface FlutterObservatoryPublisher : NSObject
 
+@property(nonatomic, readonly) NSURL* url;
+
 @end
 
 #endif  // FLUTTER_FLUTTEROBSERVATORYPUBLISHER_H_

shell/platform/darwin/ios/framework/Source/FlutterObservatoryPublisher.mm

@@ -36,6 +36,7 @@ @interface FlutterObservatoryPublisher () <NSNetServiceDelegate>
 @end
 
 @implementation FlutterObservatoryPublisher {
+  fml::scoped_nsobject<NSURL> _url;
 #if TARGET_IPHONE_SIMULATOR
   DNSServiceRef _dnsServiceRef;
 #else   // TARGET_IPHONE_SIMULATOR
@@ -46,6 +47,10 @@ @implementation FlutterObservatoryPublisher {
   std::unique_ptr<fml::WeakPtrFactory<FlutterObservatoryPublisher>> _weakFactory;
 }
 
+- (NSURL*)url {
+  return _url.get();
+}
+
 - (instancetype)init {
   self = [super init];
   NSAssert(self, @"Super must not return null on init.");
@@ -92,15 +97,14 @@ - (void)publishServiceProtocolPort:(std::string)uri {
   }
   // uri comes in as something like 'http://127.0.0.1:XXXXX/' where XXXXX is the port
   // number.
-  NSURL* url =
-      [[[NSURL alloc] initWithString:[NSString stringWithUTF8String:uri.c_str()]] autorelease];
+  _url.reset([[NSURL alloc] initWithString:[NSString stringWithUTF8String:uri.c_str()]]);
 
   NSString* serviceName =
       [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleIdentifier"];
 
   // Check to see if there's an authentication code. If there is, we'll provide
   // it as a txt record so flutter tools can establish a connection.
-  auto path = std::string{[[url path] UTF8String]};
+  auto path = std::string{[[_url path] UTF8String]};
   if (!path.empty()) {
     // Remove leading "/"
     path = path.substr(1);
@@ -116,7 +120,7 @@ - (void)publishServiceProtocolPort:(std::string)uri {
   uint32_t interfaceIndex = if_nametoindex("lo0");
   const char* registrationType = "_dartobservatory._tcp";
   const char* domain = "local.";  // default domain
-  uint16_t port = [[url port] intValue];
+  uint16_t port = [[_url port] intValue];
 
   int err = DNSServiceRegister(&_dnsServiceRef, flags, interfaceIndex, [serviceName UTF8String],
                                registrationType, domain, NULL, htons(port), txtData.length,
@@ -131,7 +135,7 @@ - (void)publishServiceProtocolPort:(std::string)uri {
   NSNetService* netServiceTmp = [[NSNetService alloc] initWithDomain:@"local."
                                                                 type:@"_dartobservatory._tcp."
                                                                 name:serviceName
-                                                                port:[[url port] intValue]];
+                                                                port:[[_url port] intValue]];
   [netServiceTmp setTXTRecordData:txtData];
   _netService.reset(netServiceTmp);
   [_netService.get() setDelegate:self];