chore(ts): duplicate the .es6 files in the facade directory to TypeScript.

Adds a gulp task which builds the .ts files (in the cjs build only).
The new files have extension .ts since they are now valid typescript.
Unfortunately until Typescript can emit System.require, we have to keep the old .es6 version
so traceur works inside the Karma preprocessor. This should be fixed soon.

gulpfile.js

@@ -1,3 +1,4 @@
+var format = require('gulp-clang-format');
 var gulp = require('gulp');
 var gulpPlugins = require('gulp-load-plugins')();
 var shell = require('gulp-shell');
@@ -7,7 +8,6 @@ var merge = require('merge');
 var path = require('path');
 
 var gulpTraceur = require('./tools/transpiler/gulp-traceur');
-
 var clean = require('./tools/build/clean');
 var transpile = require('./tools/build/transpile');
 var html = require('./tools/build/html');
@@ -143,7 +143,8 @@ var CONFIG = {
         }),
         cjs: merge(true, _COMPILER_CONFIG_JS_DEFAULT, {
           typeAssertionModule: 'rtts_assert/rtts_assert',
-          typeAssertions: true,
+          // Don't use type assertions since this is partly transpiled by typescript
+          typeAssertions: false,
           modules: 'commonjs'
         })
       },
@@ -296,6 +297,26 @@ gulp.task('build/clean.docs', clean(gulp, gulpPlugins, {
 // ------------
 // transpile
 
+gulp.task('build/transpile.ts.cjs', function() {
+  var tsResult = gulp.src(CONFIG.transpile.src.ts)
+      .pipe(sourcemaps.init())
+      .pipe(tsc({
+        target: 'ES5',
+        module: /*system.js*/'commonjs',
+        allowNonTsExtensions: false,
+        typescript: require('typescript'),
+        //declarationFiles: true,
+        noEmitOnError: true
+      }));
+  var dest = gulp.dest(CONFIG.dest.js.cjs);
+  return merge([
+    // Write external sourcemap next to the js file
+    tsResult.js.pipe(sourcemaps.write('.')).pipe(dest),
+    tsResult.js.pipe(dest),
+    tsResult.dts.pipe(dest),
+  ]);
+});
+
 gulp.task('build/transpile.js.dev.es6', transpile(gulp, gulpPlugins, {
   src: CONFIG.transpile.src.js,
   dest: CONFIG.dest.js.dev.es6,
@@ -314,8 +335,7 @@ gulp.task('build/transpile.ts.dev.es5', function() {
                        module: 'commonjs',
                        typescript: require('typescript'),
                        noEmitOnError: true
-                     }))
-                     .js;
+                     }));
   return merge([
     tsResult.js.pipe(sourcemaps.write('.'))
         .pipe(gulp.dest(CONFIG.dest.js.dev.es5)),
@@ -524,7 +544,7 @@ gulp.task('build/pubbuild.dart', pubbuild(gulp, gulpPlugins, {
 }));
 
 // ------------
-// format dart
+// formatting
 
 gulp.task('build/format.dart', rundartpackage(gulp, gulpPlugins, {
   pub: DART_SDK.PUB,
@@ -532,6 +552,11 @@ gulp.task('build/format.dart', rundartpackage(gulp, gulpPlugins, {
   args: CONFIG.formatDart.args
 }));
 
+gulp.task('check-format', function() {
+  return gulp.src(['modules/**/*.ts', '!**/typings/**/*.d.ts'])
+      .pipe(format.checkFormat('file'));
+});
+
 // ------------
 // check circular dependencies in Node.js context
 gulp.task('build/checkCircularDependencies', function (done) {
@@ -786,6 +811,9 @@ gulp.task('build.js.prod', function(done) {
 gulp.task('build.js.cjs', function(done) {
   runSequence(
     ['build/transpile.js.cjs', 'build/copy.js.cjs', 'build/multicopy.js.cjs'],
+    // Overwrite the .js.cjs transpilation with typescript outputs
+    // We still need traceur outputs everywhere else, for now.
+    'build/transpile.ts.cjs',
     ['build/linknodemodules.js.cjs'],
     'build/transformCJSTests',
     done