refactor(js2dart): refactor dart library statement

fixes #12
closes #16

tools/js2dart/spec/0-subfolder/library_spec.js

@@ -0,0 +1,3 @@
+function main() {
+  assert(true);
+}

tools/js2dart/src/compiler.js

@@ -25,14 +25,9 @@ export class Compiler extends TraceurCompiler {
     return transformer.transformAny(tree);
   }
   writeDart(tree, filename) {
-    var writer = new DartTreeWriter();
+    var writer = new DartTreeWriter(this.resolveModuleName(filename));
     writer.visitAny(tree);
-    // TODO: Do this in the writer...
+    return writer.toString();
-    var library = this.resolveModuleName(filename)
-        .replace(/\//g, '.')
-        .replace('.lib.', '.')
-        .replace(/\.dart$/, '');
-    return 'library ' + library + ';\n' + writer.toString();
   }
   // Copy of the original method to use our custom Parser
   parse(content, sourceName) {

tools/js2dart/src/dart_writer.js

@@ -4,6 +4,14 @@ import {EQUAL_EQUAL_EQUAL, OPEN_PAREN, CLOSE_PAREN, IMPORT, SEMI_COLON, STAR, OP
 import {ParseTreeWriter as JavaScriptParseTreeWriter} from 'traceur/src/outputgeneration/ParseTreeWriter';
 
 export class DartTreeWriter extends JavaScriptParseTreeWriter {
+  constructor(moduleName) {
+    super();
+    this.libName = moduleName
+        .replace(/\//g, '.')
+        .replace(/[^\w.]/, '_')
+        .replace('.lib.', '.')
+        .replace(/\.dart$/, '');
+  }
 
   // VARIABLES - types
   // ```
@@ -237,5 +245,9 @@ export class DartTreeWriter extends JavaScriptParseTreeWriter {
 
     this.writeSpace_()
   }
+
+  toString() {
+    return "library " + this.libName + ";\n" + super.toString();
+  }
 }