Allow content embedders to create AudioManager.

content/public/browser/content_browser_client.cc

Index: content/public/browser/content_browser_client.cc
diff --git a/content/public/browser/content_browser_client.cc b/content/public/browser/content_browser_client.cc
index 41e23224d7a344fdaad616cbf1c1d15f8bb8c9af..6a7bca7c1912a41464336cac03089369079a1ae3 100644
--- a/content/public/browser/content_browser_client.cc
+++ b/content/public/browser/content_browser_client.cc
@@ -102,6 +102,11 @@ bool ContentBrowserClient::ShouldSwapBrowsingInstancesForNavigation(
   return false;
 }
 
+media::ScopedAudioManagerPtr ContentBrowserClient::CreateAudioManager(
+    media::AudioLogFactory* audio_log_factory) {
+  return nullptr;
+}
+
 std::unique_ptr<media::CdmFactory> ContentBrowserClient::CreateCdmFactory() {
   return nullptr;
 }