Image aspect ratio (#1665)

* Allow user to specify an aspect ratio for various images

* added a comment on what is supported

* fixed typo

* Fixed lint and test errors

test-mocha/common/util/parse_aspect_ratio_test.js

@@ -0,0 +1,53 @@
+import assert from 'assert';
+
+import parseAspectRatio from '../../../src/common/util/parse-aspect-ratio.js';
+
+describe('parseAspectRatio', () => {
+  const ratio16by9 = { w: 16, h: 9 };
+  const ratio178 = { w: 1.78, h: 1 };
+
+  it('Parses 16x9', () => {
+    const r = parseAspectRatio('16x9');
+    assert.deepEqual(r, ratio16by9);
+  });
+
+  it('Parses 16:9', () => {
+    const r = parseAspectRatio('16:9');
+    assert.deepEqual(r, ratio16by9);
+  });
+
+  it('Parses 1.78x1', () => {
+    const r = parseAspectRatio('1.78x1');
+    assert.deepEqual(r, ratio178);
+  });
+
+  it('Parses 1.78:1', () => {
+    const r = parseAspectRatio('1.78:1');
+    assert.deepEqual(r, ratio178);
+  });
+
+  it('Parses 1.78', () => {
+    const r = parseAspectRatio('1.78');
+    assert.deepEqual(r, ratio178);
+  });
+
+  it('Skips null states', () => {
+    const r = parseAspectRatio(null);
+    assert.equal(r, null);
+  });
+
+  it('Skips empty states', () => {
+    const r = parseAspectRatio('   ');
+    assert.equal(r, null);
+  });
+
+  it('Skips invalid input', () => {
+    const r = parseAspectRatio('mary had a little lamb');
+    assert.equal(r, null);
+  });
+
+  it('Skips invalid, but close input', () => {
+    const r = parseAspectRatio('mary:lamb');
+    assert.equal(r, null);
+  });
+});