Fix install for iOS simulator, and add ability to uninstall (#4223)

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

diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index f566a14..58ae15b 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart
@@ -274,10 +274,24 @@
 
   bool _isAnyConnected() => getConnectedDevices().isNotEmpty;
 
+  bool isInstalled(String appId) {
+    return exitsHappy(<String>[
+      _xcrunPath,
+      'simctl',
+      'get_app_container',
+      'booted',
+      appId,
+    ]);
+  }
+
   void install(String deviceId, String appPath) {
     runCheckedSync(<String>[_xcrunPath, 'simctl', 'install', deviceId, appPath]);
   }
 
+  void uninstall(String deviceId, String appId) {
+    runCheckedSync(<String>[_xcrunPath, 'simctl', 'uninstall', deviceId, appId]);
+  }
+
   void launch(String deviceId, String appIdentifier, [List<String> launchArgs]) {
     List<String> args = <String>[_xcrunPath, 'simctl', 'launch', deviceId, appIdentifier];
     if (launchArgs != null)
@@ -362,6 +376,11 @@
   }
 
   @override
+  bool isAppInstalled(ApplicationPackage app) {
+    return SimControl.instance.isInstalled(app.id);
+  }
+
+  @override
   bool installApp(ApplicationPackage app) {
     try {
       IOSApp iosApp = app;
@@ -373,6 +392,16 @@
   }
 
   @override
+  bool uninstallApp(ApplicationPackage app) {
+    try {
+      SimControl.instance.uninstall(id, app.id);
+      return true;
+    } catch (e) {
+      return false;
+    }
+  }
+
+  @override
   bool isSupported() {
     if (!Platform.isMacOS) {
       _supportMessage = "Not supported on a non Mac host";
@@ -424,17 +453,6 @@
   }
 
   @override
-  bool isAppInstalled(ApplicationPackage app) {
-    try {
-      // TODO(tvolkert): This logic is wrong; simulatorHomeDirectory always exists
-      String simulatorHomeDirectory = _getSimulatorAppHomeDirectory(app);
-      return FileSystemEntity.isDirectorySync(simulatorHomeDirectory);
-    } catch (e) {
-      return false;
-    }
-  }
-
-  @override
   Future<LaunchResult> startApp(
     ApplicationPackage app,
     BuildMode mode, {
@@ -505,13 +523,7 @@
   }
 
   bool _applicationIsInstalledAndRunning(ApplicationPackage app) {
-    bool isInstalled = exitsHappy(<String>[
-      'xcrun',
-      'simctl',
-      'get_app_container',
-      'booted',
-      app.id,
-    ]);
+    bool isInstalled = isAppInstalled(app);
 
     bool isRunning = exitsHappy(<String>[
       '/usr/bin/killall',