prefer const constructor (#8292)

diff --git a/packages/flutter_tools/lib/executable.dart b/packages/flutter_tools/lib/executable.dart
index d759f9f..6891fc4 100644
--- a/packages/flutter_tools/lib/executable.dart
+++ b/packages/flutter_tools/lib/executable.dart
@@ -102,9 +102,9 @@
     // in those locations as well to see if you need a similar update there.
 
     // Seed these context entries first since others depend on them
-    context.putIfAbsent(Platform, () => new LocalPlatform());
-    context.putIfAbsent(FileSystem, () => new LocalFileSystem());
-    context.putIfAbsent(ProcessManager, () => new LocalProcessManager());
+    context.putIfAbsent(Platform, () => const LocalPlatform());
+    context.putIfAbsent(FileSystem, () => const LocalFileSystem());
+    context.putIfAbsent(ProcessManager, () => const LocalProcessManager());
     context.putIfAbsent(Logger, () => platform.isWindows ? new WindowsStdoutLogger() : new StdoutLogger());
     context.putIfAbsent(Config, () => new Config());
 
diff --git a/packages/flutter_tools/lib/src/android/android_device.dart b/packages/flutter_tools/lib/src/android/android_device.dart
index ff6389f..f4f565f 100644
--- a/packages/flutter_tools/lib/src/android/android_device.dart
+++ b/packages/flutter_tools/lib/src/android/android_device.dart
@@ -459,7 +459,7 @@
       'shell', 'am', 'broadcast', '-a', 'io.flutter.view.DISCOVER'
     ]));
 
-    return new Future<List<DiscoveredApp>>.delayed(new Duration(seconds: 1), () {
+    return new Future<List<DiscoveredApp>>.delayed(const Duration(seconds: 1), () {
       logs.cancel();
       return result;
     });
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.
diff --git a/packages/flutter_tools/lib/src/commands/daemon.dart b/packages/flutter_tools/lib/src/commands/daemon.dart
index eb8ae7a..5309be1 100644
--- a/packages/flutter_tools/lib/src/commands/daemon.dart
+++ b/packages/flutter_tools/lib/src/commands/daemon.dart
@@ -464,7 +464,7 @@
     if (app == null)
       throw "app '$appId' not found";
 
-    return app.stop().timeout(new Duration(seconds: 5)).then<bool>((_) {
+    return app.stop().timeout(const Duration(seconds: 5)).then<bool>((_) {
       return true;
     }).catchError((dynamic error) {
       _sendAppEvent(app, 'log', <String, dynamic>{ 'log': '$error', 'error': true });
diff --git a/packages/flutter_tools/lib/src/commands/test.dart b/packages/flutter_tools/lib/src/commands/test.dart
index 292bbc2..3f67022 100644
--- a/packages/flutter_tools/lib/src/commands/test.dart
+++ b/packages/flutter_tools/lib/src/commands/test.dart
@@ -97,7 +97,7 @@
   Future<bool> _collectCoverageData(CoverageCollector collector, { bool mergeCoverageData: false }) async {
     Status status = logger.startProgress('Collecting coverage information...');
     String coverageData = await collector.finalizeCoverage(
-      timeout: new Duration(seconds: 30),
+      timeout: const Duration(seconds: 30),
     );
     status.stop();
     printTrace('coverage information collection complete');
diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index ebf23f3..4da5284 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart
@@ -83,7 +83,7 @@
       connected = _isAnyConnected();
       if (!connected) {
         printStatus('Still waiting for iOS Simulator to boot...');
-        await new Future<Null>.delayed(new Duration(seconds: 1));
+        await new Future<Null>.delayed(const Duration(seconds: 1));
       }
       attempted++;
     }
diff --git a/packages/flutter_tools/lib/src/resident_runner.dart b/packages/flutter_tools/lib/src/resident_runner.dart
index 2450bd5..6bda33f 100644
--- a/packages/flutter_tools/lib/src/resident_runner.dart
+++ b/packages/flutter_tools/lib/src/resident_runner.dart
@@ -218,7 +218,7 @@
     for (int i = 0; vmService.vm.mainView == null && i < 5; i++) {
       // If the VM doesn't yet have a view, wait for one to show up.
       printTrace('Waiting for Flutter view');
-      await new Future<Null>.delayed(new Duration(seconds: 1));
+      await new Future<Null>.delayed(const Duration(seconds: 1));
       await vmService.vm.refreshViews();
     }
     currentView = vmService.vm.mainView;
@@ -354,7 +354,7 @@
       if ((currentView != null) && (currentView.uiIsolate != null)) {
         // TODO(johnmccutchan): Wait for the exit command to complete.
         currentView.uiIsolate.flutterExit();
-        await new Future<Null>.delayed(new Duration(milliseconds: 100));
+        await new Future<Null>.delayed(const Duration(milliseconds: 100));
       }
     }
     appFinished();
diff --git a/packages/flutter_tools/lib/src/run_hot.dart b/packages/flutter_tools/lib/src/run_hot.dart
index b731c32..570e762 100644
--- a/packages/flutter_tools/lib/src/run_hot.dart
+++ b/packages/flutter_tools/lib/src/run_hot.dart
@@ -314,7 +314,7 @@
     if (_devFS != null) {
       // Cleanup the devFS; don't wait indefinitely, and ignore any errors.
       await _devFS.destroy()
-        .timeout(new Duration(milliseconds: 250))
+        .timeout(const Duration(milliseconds: 250))
         .catchError((dynamic error) {
           printTrace('$error');
         });
diff --git a/packages/flutter_tools/lib/src/usage.dart b/packages/flutter_tools/lib/src/usage.dart
index ba4301d..2f4b5ec 100644
--- a/packages/flutter_tools/lib/src/usage.dart
+++ b/packages/flutter_tools/lib/src/usage.dart
@@ -96,7 +96,7 @@
     // TODO(devoncarew): This may delay tool exit and could cause some analytics
     // events to not be reported. Perhaps we could send the analytics pings
     // out-of-process from flutter_tools?
-    await _analytics.waitForLastPing(timeout: new Duration(milliseconds: 250));
+    await _analytics.waitForLastPing(timeout: const Duration(milliseconds: 250));
   }
 
   void printUsage() {