Add browser side support for reading files from renderer.

lib/browser/rpc-server.js

@@ -5,6 +5,8 @@ const electron = require('electron')
 const v8Util = process.atomBinding('v8_util')
 const {ipcMain, isPromise, webContents} = electron
 
+const fs = require('fs')
+
 const objectsRegistry = require('./objects-registry')
 
 const hasProp = {}.hasOwnProperty
@@ -235,6 +237,13 @@ ipcMain.on('ELECTRON_BROWSER_REQUIRE', function (event, module) {
   }
 })
 
+ipcMain.on('ELECTRON_BROWSER_READ_FILE', function (event, file) {
+  fs.readFile(file, (err, data) => {
+    if (err) event.returnValue = {err: err.message}
+    else event.returnValue = {data: data.toString()}
+  })
+})
+
 ipcMain.on('ELECTRON_BROWSER_GET_BUILTIN', function (event, module) {
   try {
     event.returnValue = valueToMeta(event.sender, electron[module])