dart2js: Add a header to the output of the startup emitter.

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
index e30c58b0623fbef2a47fc59f03f837e8ad49100b..4c423709a0dfb104b0727455c1d2a345803ebf03 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
@@ -34,6 +34,7 @@ import '../../util/util.dart' show
 import '../../util/uri_extras.dart' show
     relativize;
 
+import '../headers.dart';
 import '../js_emitter.dart' show AstContainer, NativeEmitter;
 
 import 'package:js_runtime/shared/embedded_names.dart' show
@@ -218,11 +219,8 @@ class ModelEmitter {
   }
 
   /// Generates a simple header that provides the compiler's build id.
-  String buildGeneratedBy(compiler) {
-    var suffix = '';
-    if (compiler.hasBuildId) suffix = ' version: ${compiler.buildId}';
-    return '// Generated by dart2js (fast startup), '
-        'the Dart to JavaScript compiler$suffix.\n';
+  String buildGeneratedBy() {
+    return new jsAst.Comment(generatedBy(compiler));

[Siggi Cherem (dart-lang), 2015/08/04 16:42:48]

should we add an argument to generatedBy so we can indicate which emitter we
used? (we used to have the "(fast startup)" as part of this header before).
Another idea is to print out all the flags/options in the header.

[floitsch, 2015/08/05 11:46:50]

I added a 'flavor' argument to 'generatedBy'. That should bring us back to what
we had before. (Even more, since I take mirrors and CSP into account).
I think we don't want to print *all* options, but it is an option, and I
wouldn't be entirely against it. Up to you.

[Siggi Cherem (dart-lang), 2015/08/05 15:53:36]

I have a feeling that all flags might be too noisy too, but there might be some
others for which it may be useful (e.g. trust-type-annotations). We don't need
to add them now.

   }
 
   /// Writes all deferred fragment's code into files.
@@ -258,7 +256,12 @@ class ModelEmitter {
             codeOutputListeners);
     outputBuffers[fragment] = mainOutput;
 
-    mainOutput.addBuffer(js.prettyPrint(code, compiler,
+    js.Program program = new js.Program([
+        new js.Comment(generatedBy(compiler)),
+        new js.Comment(HOOKS_API_USAGE),
+        code]);
+
+    mainOutput.addBuffer(js.prettyPrint(program, compiler,
         monitor: compiler.dumpInfoTask));
 
     if (shouldGenerateSourceMap) {
@@ -307,9 +310,11 @@ class ModelEmitter {
     //   deferredInitializer.current = <pretty-printed code>;
     //   deferredInitializer[<hash>] = deferredInitializer.current;
 
-    output.add('\n${deferredInitializersGlobal}.current = ');
+    js.Program program = new js.Program([
+        new js.Comment(generatedBy(compiler)),
+        js.js.statement('$deferredInitializersGlobal.current = #', code)]);
 
-    output.addBuffer(js.prettyPrint(code, compiler,
+    output.addBuffer(js.prettyPrint(program, compiler,
         monitor: compiler.dumpInfoTask));
 
     // Make a unique hash of the code (before the sourcemaps are added)