Add unit-test to check we are unducked after requesting a new audio focus

Bug: internal b/74159854
Test: unit-test ran successfully.
Change-Id: I4a66bc746a4d64abbb5f3c43dd446d350183c4bc
Reviewed-on: https://chromium-review.googlesource.com/1025278Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Chris Kuiper <ckuiper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553413}

content/browser/media/session/media_session_impl_browsertest.cc

@@ -336,6 +336,22 @@ IN_PROC_BROWSER_TEST_F(MediaSessionImplBrowserTest, AudioFocusInitialState) {
   EXPECT_FALSE(IsActive());
 }
 
+IN_PROC_BROWSER_TEST_F(MediaSessionImplBrowserTest,
+                       AddPlayerOnSuspendedFocusUnducks) {
+  auto player_observer = std::make_unique<MockMediaSessionPlayerObserver>();
+  StartNewPlayer(player_observer.get(), media::MediaContentType::Persistent);
+
+  UISuspend();
+  EXPECT_FALSE(IsActive());
+
+  SystemStartDucking();
+  EXPECT_EQ(kDuckingVolumeMultiplier, player_observer->GetVolumeMultiplier(0));
+
+  EXPECT_TRUE(
+      AddPlayer(player_observer.get(), 0, media::MediaContentType::Persistent));
+  EXPECT_EQ(kDefaultVolumeMultiplier, player_observer->GetVolumeMultiplier(0));
+}
+
 IN_PROC_BROWSER_TEST_F(MediaSessionImplBrowserTest, StartPlayerGivesFocus) {
   auto player_observer = std::make_unique<MockMediaSessionPlayerObserver>();