Add a --version option to flutter

This option just prints the current git revision.

Fixes #40

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

@@ -33,6 +33,9 @@ class FlutterCommandRunner extends CommandRunner {
         negatable: false,
         help: 'Very noisy logging, including the output of all '
             'shell commands executed.');
+    argParser.addFlag('version',
+        negatable: false,
+        help: 'Reports the version of this tool.');
     String packagesHelp;
     if (ArtifactStore.isPackageRootValid)
       packagesHelp = '\n(defaults to "${ArtifactStore.packageRoot}")';
@@ -138,6 +141,14 @@ class FlutterCommandRunner extends CommandRunner {
     if (globalResults.wasParsed('package-root'))
       ArtifactStore.packageRoot = globalResults['package-root'];
 
+    if (globalResults['version']) {
+      String revision = runSync([
+        'git', 'rev-parse', 'HEAD'
+      ], workingDirectory: ArtifactStore.flutterRoot).trim();
+      print('flutter version $revision');
+      return new Future<int>.value(0);
+    }
+
     return super.runCommand(globalResults);
   }
 

packages/flutter_tools/lib/src/process.dart

@@ -64,11 +64,12 @@ Future<Process> runDetached(List<String> cmd) {
 
 /// Run cmd and return stdout.
 /// Throws an error if cmd exits with a non-zero value.
-String runCheckedSync(List<String> cmd) =>
-    _runWithLoggingSync(cmd, checked: true);
+String runCheckedSync(List<String> cmd, { String workingDirectory }) =>
+    _runWithLoggingSync(cmd, workingDirectory: workingDirectory, checked: true);
 
 /// Run cmd and return stdout.
-String runSync(List<String> cmd) => _runWithLoggingSync(cmd);
+String runSync(List<String> cmd, { String workingDirectory }) =>
+    _runWithLoggingSync(cmd, workingDirectory: workingDirectory);
 
 /// Return the platform specific name for the given Dart SDK binary. So, `pub`
 /// ==> `pub.bat`.
@@ -76,10 +77,13 @@ String sdkBinaryName(String name) {
   return Platform.isWindows ? '$name.bat' : name;
 }
 
-String _runWithLoggingSync(List<String> cmd, {bool checked: false}) {
+String _runWithLoggingSync(List<String> cmd, {
+  bool checked: false,
+  String workingDirectory
+}) {
   _logging.info(cmd.join(' '));
   ProcessResult results =
-      Process.runSync(cmd[0], cmd.getRange(1, cmd.length).toList());
+      Process.runSync(cmd[0], cmd.getRange(1, cmd.length).toList(), workingDirectory: workingDirectory);
   if (results.exitCode != 0) {
     String errorDescription = 'Error code ${results.exitCode} '
         'returned when attempting to run command: ${cmd.join(' ')}';