prefer const constructor (#8292)

diff --git a/packages/flutter_tools/lib/src/base/config.dart b/packages/flutter_tools/lib/src/base/config.dart
index 7d38c2e..729bdd5 100644
--- a/packages/flutter_tools/lib/src/base/config.dart
+++ b/packages/flutter_tools/lib/src/base/config.dart

@@ -37,7 +37,7 @@
   }
 
   void _flushValues() {
-    String json = new JsonEncoder.withIndent('  ').convert(_values);
+    String json = const JsonEncoder.withIndent('  ').convert(_values);
     json = '$json\n';
     _configFile.writeAsStringSync(json);
   }

diff --git a/packages/flutter_tools/lib/src/base/logger.dart b/packages/flutter_tools/lib/src/base/logger.dart
index d413ac9..9f4644c 100644
--- a/packages/flutter_tools/lib/src/base/logger.dart
+++ b/packages/flutter_tools/lib/src/base/logger.dart

@@ -295,7 +295,7 @@
     stdout.write('${message.padRight(52)}     ');
     stdout.write('${_progress[0]}');
 
-    timer = new Timer.periodic(new Duration(milliseconds: 100), _callback);
+    timer = new Timer.periodic(const Duration(milliseconds: 100), _callback);
   }
 
   static final List<String> _progress = <String>['-', r'\', '|', r'/', '-', r'\', '|', '/'];

diff --git a/packages/flutter_tools/lib/src/base/process_manager.dart b/packages/flutter_tools/lib/src/base/process_manager.dart
index 382ef86..ecf8fca 100644
--- a/packages/flutter_tools/lib/src/base/process_manager.dart
+++ b/packages/flutter_tools/lib/src/base/process_manager.dart

@@ -29,7 +29,7 @@
 /// subdirectory.
 void enableRecordingProcessManager(String location) {
   Directory dir = getRecordingSink(location, _kRecordingType);
-  ProcessManager delegate = new LocalProcessManager();
+  ProcessManager delegate = const LocalProcessManager();
   RecordingProcessManager manager = new RecordingProcessManager(delegate, dir);
   addShutdownHook(() => manager.flush(finishRunningProcesses: true));
   context.setVariable(ProcessManager, manager);

diff --git a/packages/flutter_tools/lib/src/base/utils.dart b/packages/flutter_tools/lib/src/base/utils.dart
index 7fe223b..608fa7e 100644
--- a/packages/flutter_tools/lib/src/base/utils.dart
+++ b/packages/flutter_tools/lib/src/base/utils.dart

@@ -73,7 +73,7 @@
 }
 
 String toPrettyJson(Object jsonable) {
-  return new JsonEncoder.withIndent('  ').convert(jsonable) + '\n';
+  return const JsonEncoder.withIndent('  ').convert(jsonable) + '\n';
 }
 
 /// Return a String - with units - for the size in MB of the given number of bytes.