dart2js: Added support for writing dependency information into a file.

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 f6a91d73f10f84ed15452887f99e328b6f9217f4..a7c73719dc35ce68897809a434051f5a2b53c38e 100644
--- a/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -109,6 +109,12 @@ void compile(List<String> argv) {
     passThrough(argument);
   }
 
+  String getDepsOutput(Map<String, SourceFile> sourceFiles) {
+    var filenames = new List.from(sourceFiles.keys);
+    filenames.sort();
+    return Strings.join(filenames, "\n");
+  }
+
   setStrip(String argument) {
     stripArgumentSet = true;
     passThrough(argument);
@@ -283,6 +289,7 @@ void compile(List<String> argv) {
       sourceMapOut.path.substring(sourceMapOut.path.lastIndexOf('/') + 1);
   code = '$code\n//@ sourceMappingURL=${sourceMapFileName}';
   writeString(out, code);
+  writeString(new Uri.fromString('$out.deps'), getDepsOutput(sourceFiles));
   int bytesWritten = code.length;
   info('compiled $dartBytesRead bytes Dart -> $bytesWritten bytes '
        '$outputLanguage in ${relativize(cwd, out, isWindows)}');