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

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2930 matching lines @@
   }
 
   String assembleProgram() {
     measure(() {
       // Compute the required type checks to know which classes need a
       // 'is$' method.
       computeRequiredTypeChecks();
 
       computeNeededClasses();
 
-      mainBuffer.add(GENERATED_BY);
+      mainBuffer.add(buildGeneratedBy());
       addComment(HOOKS_API_USAGE, mainBuffer);
       mainBuffer.add('function ${namer.isolateName}()$_{}\n');
       mainBuffer.add('init()$N$n');
       // Shorten the code by using [namer.CURRENT_ISOLATE] as temporary.
       isolateProperties = namer.CURRENT_ISOLATE;
       mainBuffer.add(
           'var $isolateProperties$_=$_$isolatePropertiesName$N');
 
       if (!regularClasses.isEmpty ||
           !deferredClasses.isEmpty ||
@@ skipping 204 matching lines @@
     String code = buffer.getText();
     compiler.outputProvider('part', 'js')
       ..add(code)
       ..close();
     outputSourceMap(buffer, compiler.assembledCode, 'part');
   }
 
   void emitDeferredPreambleWhenEmpty(CodeBuffer buffer) {
     if (!buffer.isEmpty) return;
 
-    buffer.write(GENERATED_BY);
+    buffer.write(buildGeneratedBy());
 
     buffer.write('var old${namer.CURRENT_ISOLATE}$_='
                  '$_${namer.CURRENT_ISOLATE}$N');
 
     // TODO(ahe): This defines a lot of properties on the
     // Isolate.prototype object.  We know this will turn it into a
     // slow object in V8, so instead we should do something similar to
     // Isolate.$finishIsolateConstructor.
     buffer.write('${namer.CURRENT_ISOLATE}$_='
                  '$_${namer.isolateName}.prototype$N$n');
   }
 
+  String buildGeneratedBy() {
+    var suffix = '';
+    if (BUILD_ID != null) suffix = ' version: $BUILD_ID';
+    return '// Generated by dart2js, the Dart to JavaScript compiler$suffix.\n';
+  }
+
   String buildSourceMap(CodeBuffer buffer, SourceFile compiledFile) {
     SourceMapBuilder sourceMapBuilder =
         new SourceMapBuilder(compiler.sourceMapUri);
     buffer.forEachSourceLocation(sourceMapBuilder.addMapping);
     return sourceMapBuilder.build(compiledFile);
   }
 
   void outputSourceMap(CodeBuffer buffer, String code, String name) {
     if (!generateSourceMap) return;
     SourceFile compiledFile = new SourceFile(null, compiler.assembledCode);
     String sourceMap = buildSourceMap(mainBuffer, compiledFile);
     compiler.outputProvider(name, 'js.map')
         ..add(sourceMap)
         ..close();
   }
 
   bool isDeferred(Element element) {
     return compiler.deferredLoadTask.isDeferred(element);
   }
 
   // TODO(ahe): Remove this when deferred loading is fully implemented.
   void warnNotImplemented(Element element, String message) {
     compiler.reportMessage(compiler.spanFromSpannable(element),
                            MessageKind.GENERIC.error({'text': message}),
                            api.Diagnostic.WARNING);
   }
 }
 
-const String GENERATED_BY = """
-// Generated by dart2js, the Dart to JavaScript compiler.
-""";
-
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;
 
@@ skipping 20 matching lines @@
         functions.push(property);
       } else {
         $$[property] = element;
         classes.push(property);
         classes.push(element[""]);
       }
     }
     libraries.push([name, uri, classes, functions]);
   }
 })''';