Fix usage of Storage API in tests

We recently updated the Storage API to return AbortableOperation
instead of Promise.  These tests did not get updated at that time.
The runtime backward compatibility kept the tests from failing.

This was caught by a compiler upgrade.

Issue shaka-project#2528

Change-Id: I05f75a5e4443b111c63d7969950777db78133626

test/offline/offline_integration.js

@@ -53,7 +53,7 @@ filterDescribe('Offline', supportsStorage, () => {
   });
 
   it('stores, plays, and deletes clear content', async () => {
-    const content = await storage.store('test:sintel');
+    const content = await storage.store('test:sintel').promise;
     expect(content).toBeTruthy();
 
     const contentUri = content.offlineUri;
@@ -83,7 +83,7 @@ filterDescribe('Offline', supportsStorage, () => {
         shaka.test.TestScheme.setupPlayer(player, 'sintel-enc');
 
         storage.configure('offline.usePersistentLicense', true);
-        const content = await storage.store('test:sintel-enc');
+        const content = await storage.store('test:sintel-enc').promise;
 
         // Work around http://crbug.com/887535 in which load cannot happen right
         // after close.  Experimentally, we seem to need a ~1s delay, so we're
@@ -122,7 +122,8 @@ filterDescribe('Offline', supportsStorage, () => {
         shaka.test.TestScheme.setupPlayer(player, 'multidrm_no_init_data');
 
         storage.configure('offline.usePersistentLicense', false);
-        const content = await storage.store('test:multidrm_no_init_data');
+        const content =
+            await storage.store('test:multidrm_no_init_data').promise;
 
         const contentUri = content.offlineUri;
         goog.asserts.assert(