Respect novalidate and do not check validation or stop submission.

src/document-submit.js

@@ -54,14 +54,15 @@ export function onDocumentFormSubmit_(e) {
   user.assert(target, 'form target attribute is required: %s', form);
   user.assert(target == '_blank' || target == '_top',
       'form target=%s is invalid can only be _blank or _top: %s', target, form);
+  const shouldValidate = !form.hasAttribute('novalidate');
 
   // Safari does not trigger validation check on submission, hence we
   // trigger it manually. In other browsers this would never execute since
   // the submit event wouldn't be fired if the form is invalid.
   // TODO: This doesn't display the validation error messages. Safari makes them
   // available per input.validity object. We need to figure out a way of
   // displaying these.
-  if (form.checkValidity && !form.checkValidity()) {
+  if (shouldValidate && form.checkValidity && !form.checkValidity()) {
     e.preventDefault();
     return;
   }

test/functional/test-document-submit.js

@@ -97,6 +97,14 @@ describe('test-document-submit onDocumentFormSubmit_', () => {
     expect(tgt.checkValidity.callCount).to.equal(1);
   });
 
+  it('should not check validity if novalidate provided', () => {
+    tgt.setAttribute('novalidate', '');
+    tgt.checkValidity = sandbox.stub().returns(false);
+    onDocumentFormSubmit_(evt);
+    expect(preventDefaultSpy.callCount).to.equal(0);
+    expect(tgt.checkValidity.callCount).to.equal(0);
+  });
+
   it('should not prevent default', () => {
     tgt.checkValidity = sandbox.stub().returns(true);
     onDocumentFormSubmit_(evt);