fix(backend): report file urls for file system

Starting with v10, Node uses file urls in inspector protocol.
Breakpoints work iff file path reported using file url.
Otherwise provisional breakpoint will use path with spaces,
instead of %20.

Bug: #204

services/file_system.js

@@ -1,8 +1,20 @@
 const fs = require('fs');
+const url = require('url');
 
 const { rpc, rpc_process } = require('carlo/rpc');
 const chokidar = require('chokidar');
 
+let pathToUrl;
+if (!url.pathToFileURL) {
+  // Node 8 does not convert file paths to file urls.
+  pathToUrl = str => str;
+} else {
+  pathToUrl = function(fileName) {
+    if (url.pathToFileURL)
+      return url.pathToFileURL(fileName).toString();
+  }
+}
+
 class FileSystemHandler {
   constructor() {
     require('../lib/process_utility.js')('file_system', () => this.dispose());
@@ -26,7 +38,7 @@ class FileSystemHandler {
           setTimeout(() => client.filesChanged(events.splice(0)), 100);
         events.push({
           type: event,
-          name: name
+          name: pathToUrl(name)
         });
       }
     });
@@ -35,7 +47,7 @@ class FileSystemHandler {
 
   forceFileLoad(fileName) {
     if (fileName.startsWith(this._embedderPath) && fs.existsSync(fileName))
-      this._client.filesChanged([{type: 'add', name: fileName}]);
+      this._client.filesChanged([{type: 'add', name: pathToUrl(fileName)}]);
   }
 
   dispose() {