Add --version option to dart2js and add version information (if available) to generated code.

sdk/lib/_internal/compiler/implementation/dart2js.dart

Index: sdk/lib/_internal/compiler/implementation/dart2js.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart2js.dart b/sdk/lib/_internal/compiler/implementation/dart2js.dart
index 8d3c7da267dd827a5c2765fd143b337892ddbe12..c4242ca84a84ef86f37b7d37e74410a8ef976ae5 100644
--- a/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -86,6 +86,7 @@ void compile(List<String> argv) {
   List<String> options = new List<String>();
   bool explicitOut = false;
   bool wantHelp = false;
+  bool wantVersion = false;
   String outputLanguage = 'JavaScript';
   bool stripArgumentSet = false;
   bool analyzeOnly = false;
@@ -197,6 +198,7 @@ void compile(List<String> argv) {
                       (_) => diagnosticHandler.showWarnings = false),
     new OptionHandler('--output-type=dart|--output-type=js', setOutputType),
     new OptionHandler('--verbose', setVerbose),
+    new OptionHandler('--version', (_) => wantVersion = true),
     new OptionHandler('--library-root=.+', setLibraryRoot),
     new OptionHandler('--out=.+|-o.+', setOutput),
     new OptionHandler('--allow-mock-compilation', passThrough),
@@ -235,7 +237,9 @@ void compile(List<String> argv) {
   ];
 
   parseCommandLine(handlers, argv);
-  if (wantHelp) helpAndExit(diagnosticHandler.verbose);
+  if (wantHelp || wantVersion) {
+    helpAndExit(wantHelp, wantVersion, diagnosticHandler.verbose);
+  }
 
   if (outputLanguage != OUTPUT_LANGUAGE_DART && stripArgumentSet) {
     helpAndFail('Error: --force-strip may only be used with '
@@ -413,6 +417,9 @@ Supported options:
   -v, --verbose
     Display verbose information.
 
+  --version
+    Display version information.
+
   -p<path>, --package-root=<path>
     Where to find packages, that is, "package:..." imports.
 
@@ -487,11 +494,19 @@ be removed in a future version:
 '''.trim());
 }
 
-void helpAndExit(bool verbose) {
-  if (verbose) {
-    verboseHelp();
-  } else {
-    help();
+void helpAndExit(bool wantHelp, bool wantVersion, bool verbose) {
+  if (wantVersion) {
+    var version = (BUILD_ID == null)
+        ? '<non-SDK build>'
+        : BUILD_ID;
+    print('Dart-to-JavaScript compiler (dart2js) version: $version');
+  }
+  if (wantHelp) {
+    if (verbose) {
+      verboseHelp();
+    } else {
+      help();
+    }
   }
   exit(0);
 }