Fix race condition locating observatory port on iOS (#6090)

Ensure that we're monitoring logs before we launch the app on the
device. This prevents the case where we start monitoring after the ports
have already been logged.

Also update the regex to use an optional capture group.

packages/flutter_tools/lib/src/ios/devices.dart

diff --git a/packages/flutter_tools/lib/src/ios/devices.dart b/packages/flutter_tools/lib/src/ios/devices.dart
index ac2b816..3e4c378 100644
--- a/packages/flutter_tools/lib/src/ios/devices.dart
+++ b/packages/flutter_tools/lib/src/ios/devices.dart
@@ -249,6 +249,16 @@
       // ports post launch.
       printTrace("Debugging is enabled, connecting to observatory and the diagnostic server");
 
+      Future<int> forwardObsPort = _acquireAndForwardPort(ProtocolDiscovery.kObservatoryService,
+                                                          debuggingOptions.observatoryPort);
+      Future<int> forwardDiagPort;
+      if (debuggingOptions.buildMode == BuildMode.debug) {
+        forwardDiagPort = _acquireAndForwardPort(ProtocolDiscovery.kDiagnosticService,
+                                                 debuggingOptions.diagnosticPort);
+      } else {
+        forwardDiagPort = new Future<int>.value(null);
+      }
+
       Future<int> launch = runCommandAndStreamOutput(launchCommand, trace: true);
 
       List<int> ports = await launch.then((int result) async {
@@ -260,17 +270,6 @@
         }
 
         printTrace("Application launched on the device. Attempting to forward ports.");
-
-        Future<int> forwardObsPort = _acquireAndForwardPort(ProtocolDiscovery.kObservatoryService,
-                                                            debuggingOptions.observatoryPort);
-        Future<int> forwardDiagPort;
-        if (debuggingOptions.buildMode == BuildMode.debug) {
-          forwardDiagPort = _acquireAndForwardPort(ProtocolDiscovery.kDiagnosticService,
-                                                   debuggingOptions.diagnosticPort);
-        } else {
-          forwardDiagPort = new Future<int>.value(null);
-        }
-
         return Future.wait(<Future<int>>[forwardObsPort, forwardDiagPort]);
       });
 
@@ -435,7 +434,7 @@
   //
   // iOS 9 format:  Runner[297] <Notice>:
   // iOS 10 format: Runner(libsystem_asl.dylib)[297] <Notice>:
-  static final RegExp _runnerRegex = new RegExp(r'Runner[(.*)]\[[\d]+\] <[A-Za-z]+>: ');
+  static final RegExp _runnerRegex = new RegExp(r'Runner(\(.*\))?\[[\d]+\] <[A-Za-z]+>: ');
 
   void _onLine(String line) {
     Match match = _runnerRegex.firstMatch(line);