Add some print statements to smooth first run

This patch adds a couple print statements to explain why the first run of
`flutter start` takes a while. (We need to download the APK and install it on
the device.)

packages/flutter_tools/lib/src/artifacts.dart

@@ -34,7 +34,7 @@ class ArtifactStore {
   }
 
   static Future _downloadFile(String url, File file) async {
-    _logging.fine('Downloading $url to ${file.path}');
+    print('Downloading $url to ${file.path}.');
     HttpClient httpClient = new HttpClient();
     HttpClientRequest request = await httpClient.getUrl(Uri.parse(url));
     HttpClientResponse response = await request.close();

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

@@ -37,8 +37,8 @@ class InitCommand extends Command {
 
     String message = '''All done! To run your application:
 
-  cd ${out.path}
-  ./packages/flutter/sky_tool start
+  \$ cd ${out.path}
+  \$ flutter start --checked
 ''';
 
     if (argResults['pub']) {

packages/flutter_tools/lib/src/device.dart

@@ -720,6 +720,7 @@ class AndroidDevice extends Device {
       return false;
     }
 
+    print('Installing ${app.name} on device.');
     runCheckedSync([adbPath, 'install', '-r', app.localPath]);
 
     Directory tempDir = Directory.systemTemp;