clear logs on app launch

packages/flutter_tools/lib/src/commands/listen.dart

@@ -11,8 +11,8 @@ import 'start.dart';
 
 class ListenCommand extends StartCommandBase {
   final String name = 'listen';
-  final String description = 'Listen for changes to files and reload the running app on all connected devices. (Android only.)'
-      'By default, only listens to "./" and "./lib/". To listen to additional directories, list them on the command line.';
+  final String description = 'Listen for changes to files and reload the running app on all connected devices (Android only).'
+      ' By default, only listens to "./" and "./lib/". To listen to additional directories, list them on the command line.';
 
   /// Only run once.  Used for testing.
   final bool singleRun;

packages/flutter_tools/lib/src/commands/start.dart

@@ -46,7 +46,12 @@ abstract class StartCommandBase extends FlutterCommand {
     }
   }
 
-  Future<int> startApp({ bool stop: true, bool install: true, bool poke: false }) async {
+  Future<int> startApp({
+    bool stop: true,
+    bool install: true,
+    bool poke: false,
+    bool clearLogs: false
+  }) async {
 
     String mainPath = findMainDartFile(argResults['target']);
     if (!FileSystemEntity.isFileSync(mainPath)) {
@@ -63,7 +68,7 @@ abstract class StartCommandBase extends FlutterCommand {
       stopper.inheritFromParent(this);
       stopper.stop();
     }
- 
+
     if (install) {
       logging.fine('Running install command.');
       InstallCommand installer = new InstallCommand();
@@ -90,7 +95,8 @@ abstract class StartCommandBase extends FlutterCommand {
                                         poke: poke,
                                         checked: argResults['checked'],
                                         traceStartup: argResults['trace-startup'],
-                                        route: argResults['route']))
+                                        route: argResults['route'],
+                                        clearLogs: clearLogs))
             startedSomething = true;
         }
       );
@@ -110,12 +116,15 @@ abstract class StartCommandBase extends FlutterCommand {
 
 class StartCommand extends StartCommandBase {
   final String name = 'start';
-  final String description = 'Start your Flutter app on attached devices. (Android only.)';
+  final String description = 'Start your Flutter app on attached devices (Android only).';
 
   StartCommand() {
     argParser.addFlag('poke',
         negatable: false,
         help: 'Restart the connection to the server.');
+    argParser.addFlag('clear-logs',
+        defaultsTo: true,
+        help: 'Clear log history before starting the app.');
   }
 
   @override
@@ -128,9 +137,10 @@ class StartCommand extends StartCommandBase {
     ]);
 
     bool poke = argResults['poke'];
+    bool clearLogs = argResults['clear-logs'];
 
     // Only stop and reinstall if the user did not specify a poke
-    int result = await startApp(stop: !poke, install: !poke, poke: poke);
+    int result = await startApp(stop: !poke, install: !poke, poke: poke, clearLogs: clearLogs);
 
     logging.fine('Finished start command.');
     return result;

packages/flutter_tools/lib/src/device.dart

@@ -776,10 +776,11 @@ class AndroidDevice extends Device {
   }
 
   bool startBundle(AndroidApk apk, String bundlePath, {
-    bool poke,
-    bool checked,
-    bool traceStartup,
-    String route
+    bool poke: false,
+    bool checked: true,
+    bool traceStartup: false,
+    String route,
+    bool clearLogs: false
   }) {
     logging.fine('$this startBundle');
 
@@ -791,6 +792,9 @@ class AndroidDevice extends Device {
     if (!poke)
       _forwardObservatoryPort();
 
+    if (clearLogs)
+      this.clearLogs();
+
     String deviceTmpPath = '/data/local/tmp/dev.flx';
     runCheckedSync(adbCommandForDevice(['push', bundlePath, deviceTmpPath]));
     List<String> cmd = adbCommandForDevice([
@@ -801,7 +805,7 @@ class AndroidDevice extends Device {
     if (checked)
       cmd.addAll(['--ez', 'enable-checked-mode', 'true']);
     if (traceStartup)
-        cmd.addAll(['--ez', 'trace-startup', 'true']);
+      cmd.addAll(['--ez', 'trace-startup', 'true']);
     if (route != null)
       cmd.addAll(['--es', 'route', route]);
     cmd.add(apk.launchActivity);