PaymentHandler: Rename PaymentAppManager to PaymentManager.

third_party/WebKit/LayoutTests/http/tests/payments/resources/payment-app.js

 importScripts('/resources/testharness.js');
 
 test(function() {
-    assert_idl_attribute(registration, 'paymentAppManager', 'One-shot PaymentAppManager needs to be exposed on the registration.');
+    assert_idl_attribute(registration, 'paymentManager', 'One-shot PaymentManager needs to be exposed on the registration.');
 
-    assert_inherits(registration.paymentAppManager, 'setManifest');
-    assert_inherits(registration.paymentAppManager, 'getManifest');
-}, 'PaymentAppManager should be exposed and have the expected interface.');
+    assert_inherits(registration.paymentManager, 'setManifest');
+    assert_inherits(registration.paymentManager, 'getManifest');
+}, 'PaymentManager should be exposed and have the expected interface.');