Add nicer logging/reporting to dev/update_packages.dart

Makes it more obvious where we are spending our time on Travis.

Also added travis caching for the global pub cache to
speed this up!  Modeled what dartdoc does:
https://github.com/dart-lang/dartdoc/blob/master/.travis.yml#L13

@Hixie

.travis.yml

@@ -13,3 +13,6 @@ before_script:
   - ./travis/setup.sh
 script:
   - ./travis/test.sh
+cache:
+  directories:
+  - $HOME/.pub-cache

dev/update_packages.dart

@@ -6,27 +6,40 @@
 import 'dart:io';
 
 final String binaryName = Platform.isWindows ? 'pub.bat' : 'pub';
-void update(Directory directory, bool upgrade) {
+int runPub(Directory directory, List<String> pubArgs) {
+  int updateCount = 0;
   for (FileSystemEntity dir in directory.listSync()) {
     if (dir is Directory) {
-      print("Updating ${dir.path}...");
+      updateCount++;
+      Stopwatch timer = new Stopwatch()..start();
+      stdout.write("Updating ${dir.path}...");
       ProcessResult result = Process.runSync(
         binaryName,
-        [ upgrade ? 'upgrade' : 'get' ],
+        pubArgs,
         workingDirectory: dir.path
       );
+      timer.stop();
+      stdout.write(" (${timer.elapsedMilliseconds} ms)");
       if (result.exitCode != 0) {
         print("... failed with exit code ${result.exitCode}.");
         print(result.stdout);
         print(result.stderr);
+      } else {
+        stdout.write("\n");
       }
     }
   }
+  return updateCount;
 }
 
 void main(List<String> arguments) {
+  Stopwatch timer = new Stopwatch()..start();
   bool upgrade = arguments.length > 0 && arguments[0] == '--upgrade';
   String FLUTTER_ROOT = new File(Platform.script.toFilePath()).parent.parent.path;
-  update(new Directory("$FLUTTER_ROOT/packages"), upgrade);
-  update(new Directory("$FLUTTER_ROOT/examples"), upgrade);
+  List<String> pubArgs = [ upgrade ? 'upgrade' : 'get' ];
+  int count = 0;
+  count += runPub(new Directory("$FLUTTER_ROOT/packages"), pubArgs);
+  count += runPub(new Directory("$FLUTTER_ROOT/examples"), pubArgs);
+  String command = "$binaryName ${pubArgs.join(' ')}";
+  print("Ran \"$command\" $count times in ${timer.elapsedMilliseconds} ms");
 }