Add `autoOrientImage` module

This module exposes `loadImage` with a `Promise` based interface and pre-
populates `orientation: true` option to auto-orient input. Returns data URL
as string.

The module uses a named export as refactoring references of modules with
`default` (`module.exports`) export references can be error-prone.
See: https://basarat.gitbooks.io/typescript/docs/tips/defaultIsBad.html

js/modules/autoOrientImage.js

@@ -0,0 +1,27 @@
+// File | Blob | URLString -> LoadImageOptions -> Promise<DataURLString>
+//
+// Documentation for `options`:
+// https://github.com/blueimp/JavaScript-Load-Image/tree/v2.18.0#options
+exports.autoOrientImage = (fileOrBlobOrURL, options) => {
+  const optionsWithAutoOrient = Object.assign(
+    {},
+    options, {
+      canvas: true,
+      orientation: true,
+    }
+  );
+
+  return new Promise((resolve, reject) => {
+    window.loadImage(fileOrBlobOrURL, canvasOrError => {
+      if (canvasOrError.type === 'error') {
+        const error = canvasOrError;
+        reject(error);
+        return;
+      }
+
+      const canvas = canvasOrError;
+      const dataURL = canvas.toDataURL();
+      resolve(dataURL);
+    }, optionsWithAutoOrient);
+  });
+};

preload.js

@@ -71,6 +71,8 @@
   window.nodeNotifier = require('node-notifier');
 
   window.loadImage = require('blueimp-load-image');
+  const {autoOrientImage} = require('./js/modules/autoOrientImage');
+  window.autoOrientImage = autoOrientImage;
 
   // We pull this in last, because the native module involved appears to be sensitive to
   //   /tmp mounted as noexec on Linux.